Update GcmHeader types

[eddyashton]

Side effect of #3569 was introducing a new public-header-includes-private chain from symmetric_key.h. This was because GcmHeader was templated on the IV_SIZE, so the implementation details need to be public. I've refactored that so GcmHeader is no longer templated (but still fixed-size by construction), and derived a supporting type for the users that still want statically known IV sizes.

Additionally I've simplified this public interface a little, moving the Tx-encryption specifics (interpreting the IV as a seqno + term + snapshot-bit) out of the public definition, and closer to where it's used.

[ghost]

gcm_private_impl@42104 aka 20220218.17 vs main ewma over 20 builds from 41777 to 42094

Click to see table

main

build_id	build_number	tpcc_sgx_cft^	tpcc_sgx_cft_mem	ls_sgx_cft^	ls_sgx_cft_mem	ls_jwt_sgx_cft^	ls_jwt_sgx_cft_mem	ls_js_sgx_cft^	ls_js_sgx_cft_mem	ls_v8_sgx_cft^	ls_v8_sgx_cft_mem	ls_full_js_sgx_cft^	ls_full_js_sgx_cft_mem	ls_full_v8_sgx_cft^	ls_full_v8_sgx_cft_mem	ls_js_jwt_sgx_cft^	ls_js_jwt_sgx_cft_mem	hist_sgx_cft^	RB put (/s)^	CHAMP put (/s)^	RB get (/s)^	CHAMP get (/s)^
41777	20220214.18	5865.45	8.97885e+07	19688.8	1.58639e+07	5560.78	1.56017e+07	2517.87	1.03588e+07	1615.71	1.63975e+08	2147.62	1.00967e+07	1453.37	9.76528e+07	1962.5	9.31027e+06	17754	886267	1.38687e+06	9.24597e+06	3.59923e+07
41783	20220214.20	5952.36	9.08371e+07	20144.7	1.6126e+07	5624.12	1.56017e+07	2549.75	1.00967e+07	1671.19	1.64237e+08	2164.37	9.57242e+06	1447.8	9.81771e+07	1888.25	9.04813e+06	18738.6	887920	1.34701e+06	9.21273e+06	3.61199e+07
41790	20220215.2	6048.05	9.03128e+07	19906	1.71746e+07	5686.33	1.58639e+07	2544.02	1.03588e+07	1642.59	1.63451e+08	2170.01	9.83456e+06	1471.8	9.87014e+07	1921.84	9.31027e+06	20003.4	924058	1.35736e+06	9.19619e+06	3.66369e+07
41819	20220215.13	5961.57	9.08371e+07	20085.7	1.6126e+07	5614.26	1.53396e+07	2549.07	1.2456e+07	1660.44	1.61354e+08	2170.95	9.83456e+06	1477.95	9.87014e+07	1975.43	9.04813e+06	20036.4	913181	1.37191e+06	9.36867e+06	3.5189e+07
41839	20220215.20	6037.49	9.10992e+07	20014.2	1.6126e+07	5693.99	1.56017e+07	2649.45	1.03588e+07	1677.76	1.63713e+08	2164.08	1.00967e+07	1505.08	9.81771e+07	1932.56	9.57242e+06	19848.4	895881	1.35628e+06	9.35578e+06	3.58042e+07
41851	20220215.25	6003.55	9.08371e+07	19996.4	1.58639e+07	5619.51	1.56017e+07	2531.12	1.03588e+07	1630.16	1.63975e+08	2162.59	1.00967e+07	1443.5	9.87014e+07	1934.6	9.57242e+06	18235	895333	1.39357e+06	9.44645e+06	3.65056e+07
41861	20220215.29	5995.07	9.03128e+07	19962.2	1.63882e+07	5640.8	1.56017e+07	2537.86	1.35046e+07	1625.91	1.63451e+08	2111.27	1.00967e+07	1469.38	9.79149e+07	1970.53	9.31027e+06	20076.6	888073	1.39642e+06	9.22514e+06	3.56168e+07
41879	20220215.35	5867.64	8.97885e+07	19734.9	1.6126e+07	5682.42	1.56017e+07	2527.3	1.0621e+07	1629.15	1.63713e+08	2051.63	1.21939e+07	1463.9	9.89635e+07	1961.04	9.04813e+06	19070.9	907997	1.35315e+06	9.36867e+06	3.65714e+07
41919	20220215.49	5659.44	9.05749e+07	18947.4	1.63882e+07	5526.55	1.56017e+07	2472.27	9.83456e+06	1572.28	1.63451e+08	2138.1	9.04813e+06	1423.79	9.87014e+07	1914.34	9.31027e+06	18735.6	877457	1.34356e+06	9.0419e+06	3.50679e+07
41940	20220215.57	5976.65	9.26721e+07	20000.8	1.63882e+07	5684.32	1.56017e+07	2524.82	1.03588e+07	1661.56	1.64237e+08	2109.61	1.03588e+07	1475.98	9.87014e+07	1878.96	1.11453e+07	21970.4	904869	1.3768e+06	9.27112e+06	3.58669e+07
41943	20220216.1	6053.86	9.10992e+07	19977.7	1.63882e+07	5632.89	1.6126e+07	2524.46	1.0621e+07	1663.47	1.63975e+08	2166.73	1.00967e+07	1482.81	9.89635e+07	1969.38	9.31027e+06	17362.9	879418	1.40148e+06	9.40308e+06	3.58669e+07
41971	20220217.1	5961.12	9.00506e+07	19956.7	1.66503e+07	5662.83	1.56017e+07	2545.28	1.03588e+07	1655.01	1.62402e+08	2185.9	9.83456e+06	1487.66	9.87014e+07	1984.7	9.31027e+06	19455.6	908722	1.38303e+06	9.21688e+06	3.67019e+07
42010	20220217.15	6000.5	9.03128e+07	19673.9	1.69124e+07	5661.87	1.58639e+07	2400.44	1.03588e+07	1637.96	1.63451e+08	2230.07	9.57242e+06	1478.06	9.87014e+07	1966.5	9.31027e+06	17686.2	903869	1.38602e+06	9.30905e+06	3.63766e+07
42017	20220217.18	5901.08	9.13613e+07	19836	1.74367e+07	5518.43	1.56017e+07	2533.56	1.00967e+07	1638.9	1.62665e+08	2149.57	9.83456e+06	1450.01	9.87014e+07	1937.65	1.11453e+07	19972	901482	1.39044e+06	9.33876e+06	3.58669e+07
42040	20220217.26	5837.37	8.97885e+07	19762.9	1.66503e+07	5636.59	1.56017e+07	2538.87	1.0621e+07	1644.94	1.63189e+08	2163.74	1.00967e+07	1462.36	9.76528e+07	1964.24	9.83456e+06	20054.6	903595	1.37394e+06	9.28798e+06	3.57417e+07
42063	20220218.1	5836.31	8.97885e+07	19979.8	1.58639e+07	5654.85	1.58639e+07	2534.49	1.03588e+07	1652.36	1.645e+08	2161.46	9.83456e+06	1461.92	9.89635e+07	2018.57	8.78598e+06	21834.2	903032	1.37219e+06	9.22934e+06	3.58663e+07
42069	20220218.3	6118.04	9.16235e+07	18538.9	1.6126e+07	5573.33	1.58639e+07	2525.65	1.03588e+07	1656.49	1.64237e+08	2162.93	1.00967e+07	1425.53	9.87014e+07	1964.72	9.31027e+06	20305.9	906268	1.41857e+06	9.4074e+06	3.54939e+07
42075	20220218.5	5645.07	9.05749e+07	19205.9	1.66503e+07	5589.19	1.56017e+07	2531.81	1.0621e+07	1635.21	1.61878e+08	2160.44	1.03588e+07	1467.45	9.87014e+07	1968.46	9.31027e+06	18034.8	922557	1.38107e+06	9.4074e+06	3.64413e+07
42089	20220218.11	5970.53	9.10992e+07	19748.5	1.63882e+07	5613.78	1.58639e+07	2526.78	1.08831e+07	1620.27	1.63975e+08	2114.89	9.83456e+06	1422.61	9.76528e+07	1907.5	9.31027e+06	18943.2	910096	1.38537e+06	9.25855e+06	3.57417e+07
42094	20220218.13	5968.92	9.00506e+07	20004.6	1.6126e+07	5685.72	1.56017e+07	2542.61	1.0621e+07	1659.39	1.61354e+08	2167.73	1.00967e+07	1477.41	9.92257e+07	1972.93	9.04813e+06	19940.9	910262	1.37829e+06	9.20445e+06	3.58036e+07

gcm_private_impl

build_id	build_number	tpcc_sgx_cft^	tpcc_sgx_cft_mem	ls_sgx_cft^	ls_sgx_cft_mem	ls_jwt_sgx_cft^	ls_jwt_sgx_cft_mem	ls_js_sgx_cft^	ls_js_sgx_cft_mem	ls_v8_sgx_cft^	ls_v8_sgx_cft_mem	ls_full_js_sgx_cft^	ls_full_js_sgx_cft_mem	ls_full_v8_sgx_cft^	ls_full_v8_sgx_cft_mem	ls_js_jwt_sgx_cft^	ls_js_jwt_sgx_cft_mem	hist_sgx_cft^	RB put (/s)^	CHAMP put (/s)^	RB get (/s)^	CHAMP get (/s)^
42104	20220218.17	5935.22	9.05749e+07	19544.8	1.63882e+07	5648.27	1.50774e+07	2477.8	1.00967e+07	1573.65	1.63713e+08	2130.84	1.00967e+07	1471.53	9.73907e+07	1963.33	9.31027e+06	20144.7	888138	1.39459e+06	9.3685e+06	3.56788e+07