Populate ms_hs_date in GetModSummary rule

[pepeiborra]

This is a straightforward fix that came up during haskell/haskell-language-server#191

[digitalasset-cla]

All committers have signed the CLA.

[pepeiborra]

I extended this change in the following directions:

1. Platform dependent code to convert FileVersion to Maybe UTCTime. Further improvements possible in Mingw platforms to avoid UTCTime -> FileVersion -> Maybe UTCTime
2. Add timestamps to the ModSummary code path for parsing: we need both parsing and interfaces mod summaries to have timestamps
3. Added a new Shake rule ModSummaryWithoutTimestamp to preserve the existing early cutoff semantics and avoid a perf regression.

I tested the changes with the Eval plugin in haskell-language-server, branch: http://github.com/pepeiborra/ide/tree/eval

Please take another look and let me know

[pepeiborra]

Benchmarks showing no perf regressions (in non-mingw): https://github.com/pepeiborra/ghcide/tree/getmodsummary-modtime-benchmarks/bench-hist

version	name	experiment	maxResidency	startup	setup
upstream	code actions	0.9317128790000001	209MB	10.373322118	1.151683226
HEAD	code actions	0.8851059400000001	210MB	10.62859897	1.1537126960000001
upstream	code actions after edit	30.920481852	209MB	9.899097365000001	0.0
HEAD	code actions after edit	31.179141626000003	209MB	10.358541327000001	0.0
upstream	completions after edit	8.112460716000001	171MB	10.121257906	0.0
HEAD	completions after edit	8.267294747000001	179MB	10.808873808000001	0.0
upstream	documentSymbols after edit	3.065205062	172MB	10.184797083000001	0.0
HEAD	documentSymbols after edit	2.86471839	165MB	11.014139748	0.0
upstream	edit	47.011598097000004	181MB	12.018539653000001	0.0
HEAD	edit	46.720616624	181MB	10.239523371	0.0
upstream	getDefinition	0.957393601	172MB	9.946836806	0.0
HEAD	getDefinition	0.9199532	177MB	10.826650862000001	0.0
upstream	hover	0.569961916	172MB	11.371499782	0.0
HEAD	hover	0.24769026000000002	173MB	10.040305052	0.0
upstream	hover after edit	1.5125140590000001	171MB	10.11517897	0.0
HEAD	hover after edit	1.533573115	180MB	10.872858544000001	0.0

[cocreature]

Thanks! Looks good to me with two small comments.

[cocreature]

Thanks!