Add ruby_upb_alloc using xrealloc/xfree so Ruby GC is aware of allocated memory for Arenas.

[zhangskz]

Add ruby-specific upb_alloc using xrealloc/xfree for use in Arena_alloc so Ruby GC is aware of allocated memory. Fixes #9546.

Since ruby is now aware of memory allocated for ruby arena object, RB_GC_GUARD must be used to protect from premature GC in cases where C sees no references to the ruby arena object (though upb may still be using the associated memory).

Results using script from #9467.

Before:

Encoded payload length: 1888895
Memory before test loop:    rss 121,432    vsz 1,253,468
Starting test loop...
1..200:  25.3 ms/rep    rss 1,440,180    vsz 3,083,840
201..400:  28.4 ms/rep    rss 2,765,192    vsz 4,926,608
401..600:  20.1 ms/rep    rss 4,090,208    vsz 6,769,592
601..800:  18.5 ms/rep    rss 5,415,224    vsz 8,612,568
801..1000:  18.9 ms/rep    rss 6,739,976    vsz 10,455,544
1001..1200:  18.9 ms/rep    rss 8,064,992    vsz 12,298,868
1201..1400:  18.8 ms/rep    rss 9,390,272    vsz 14,142,024
1401..1600:  18.4 ms/rep    rss 10,715,288    vsz 15,985,180
1601..1800:  18.8 ms/rep    rss 12,040,304    vsz 17,828,336
1801..2000:  19.0 ms/rep    rss 13,365,320    vsz 19,671,492
2001..2200:  19.1 ms/rep    rss 14,690,600    vsz 21,514,984
2201..2400:  18.7 ms/rep    rss 16,015,616    vsz 23,358,144
2401..2600:  18.6 ms/rep    rss 17,340,632    vsz 25,201,300
2601..2800:  19.9 ms/rep    rss 18,665,648    vsz 27,044,456
2801..3000:  18.9 ms/rep    rss 19,990,664    vsz 28,887,612
3001..3200:  18.9 ms/rep    rss 21,315,680    vsz 30,730,768
3201..3400:  18.6 ms/rep    rss 22,640,960    vsz 32,573,924
3401..3600:  18.5 ms/rep    rss 23,965,976    vsz 34,417,080
3601..3800:  18.6 ms/rep    rss 25,290,992    vsz 36,260,236
3801..4000:  18.8 ms/rep    rss 26,616,008    vsz 38,103,392
4001..4200:  18.5 ms/rep    rss 27,941,288    vsz 39,947,220
4201..4400:  18.0 ms/rep    rss 29,266,304    vsz 41,790,376
4401..4600:  18.2 ms/rep    rss 30,591,320    vsz 43,633,536
4601..4800:  17.3 ms/rep    rss 31,916,600    vsz 45,476,692
4801..5000:  19.4 ms/rep    rss 33,241,616    vsz 47,319,848
Total test time: 97.5 seconds
Memory after final GC:    rss 33,241,616    vsz 47,319,848

After (gem "google-protobuf", :path => "~/protobuf/ruby/"):

Encoded payload length: 1888895
Memory before test loop:    rss 43,976    vsz 1,168,080
Starting test loop...
1..200:  3.6 ms/rep    rss 134,880    vsz 1,260,180
201..400:  2.7 ms/rep    rss 134,880    vsz 1,260,180
401..600:  2.7 ms/rep    rss 134,880    vsz 1,260,180
601..800:  2.7 ms/rep    rss 134,880    vsz 1,260,180
801..1000:  2.9 ms/rep    rss 81,368    vsz 1,204,764
1001..1200:  2.9 ms/rep    rss 90,888    vsz 1,215,924
1201..1400:  2.9 ms/rep    rss 88,280    vsz 1,214,104
1401..1600:  2.9 ms/rep    rss 67,688    vsz 1,191,084
1601..1800:  3.0 ms/rep    rss 82,732    vsz 1,213,476
1801..2000:  3.0 ms/rep    rss 90,028    vsz 1,215,060
2001..2200:  3.0 ms/rep    rss 90,736    vsz 1,218,912
2201..2400:  2.9 ms/rep    rss 92,932    vsz 1,218,156
2401..2600:  3.0 ms/rep    rss 89,500    vsz 1,214,700
2601..2800:  3.0 ms/rep    rss 91,276    vsz 1,218,156
2801..3000:  3.6 ms/rep    rss 92,596    vsz 1,218,372
3001..3200:  4.0 ms/rep    rss 92,764    vsz 1,218,084
3201..3400:  3.3 ms/rep    rss 92,668    vsz 1,218,156
3401..3600:  3.5 ms/rep    rss 89,500    vsz 1,214,700
3601..3800:  3.9 ms/rep    rss 89,416    vsz 1,215,240
3801..4000:  4.1 ms/rep    rss 120,416    vsz 1,250,892
4001..4200:  3.2 ms/rep    rss 120,416    vsz 1,250,892
4201..4400:  2.7 ms/rep    rss 120,416    vsz 1,250,892
4401..4600:  2.7 ms/rep    rss 120,416    vsz 1,250,892
4601..4800:  2.7 ms/rep    rss 120,416    vsz 1,250,892
4801..5000:  2.7 ms/rep    rss 120,416    vsz 1,250,892
Total test time: 16.0 seconds
Memory after final GC:    rss 120,416    vsz 1,250,892

[haberman]

Looks great! Could you put before/after measurements for the benchmark into the PR description, to make the impact even more clear?