P/Invoke TickCount64 for .NET Standard on Windows

[bitfaster]

Note; this introduces a test hole: there are currently no tests that verify .NET standard when it is not running on Windows (we only execute NET4.8 on Windows to test .NET Standard). Since code coverage analysis only runs for .NET Core build targets, this is not observable in the code coverage report.

[bitfaster]

Static bool check for OS is elided by the JIT on .NET 4.8.

Original code (v2.5.0 baseline)

.NET Framework 4.8.1 (4.8.9232.0), X64 RyuJIT VectorSize=256

; BitFaster.Caching.Benchmarks.TimeBenchmarks.DurationSinceEpoch()
       sub       rsp,28
;             return Duration.SinceEpoch();
;             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
       call      System.Diagnostics.Stopwatch.GetTimestamp()
       nop
       add       rsp,28
       ret
; Total bytes of code 15

Raw P/Invoke

.NET Framework 4.8.1 (4.8.9232.0), X64 RyuJIT VectorSize=256

; BitFaster.Caching.Benchmarks.TimeBenchmarks.PInvokeTickCount64()
       sub       rsp,28
       call      BitFaster.Caching.Benchmarks.TickCount64.GetTickCount64()
       nop
       add       rsp,28
       ret
; Total bytes of code 15

PInvoke method
BitFaster.Caching.Benchmarks.TickCount64.GetTickCount64()

New code (static bool check, then pinvoke)

.NET Framework 4.8.1 (4.8.9232.0), X64 RyuJIT VectorSize=256

; BitFaster.Caching.Benchmarks.TimeBenchmarks.DurationSinceEpoch()
       sub       rsp,28
;             return Duration.SinceEpoch();
;             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
       call      BitFaster.Caching.Duration.GetTickCount64()
       nop
       add       rsp,28
       ret
; Total bytes of code 15

PInvoke method
BitFaster.Caching.Duration.GetTickCount64()

[bitfaster]

Duration.SinceEpoch is almost identical to raw p/invoke:

BenchmarkDotNet v0.13.12, Windows 11 (10.0.22621.3447/22H2/2022Update/SunValley2)
Intel Xeon W-2133 CPU 3.60GHz, 1 CPU, 12 logical and 6 physical cores
  [Host]             : .NET Framework 4.8.1 (4.8.9232.0), X64 RyuJIT VectorSize=256
  .NET Framework 4.8 : .NET Framework 4.8.1 (4.8.9232.0), X64 RyuJIT VectorSize=256

Method	Runtime	Mean	Error	StdDev	Ratio	Code Size
DateTimeUtcNow	.NET Framework 4.8	58.1916 ns	0.5423 ns	0.4529 ns	1.000	1,048 B
DateTimeOffsetUtcNow	.NET Framework 4.8	69.9188 ns	0.2347 ns	0.1832 ns	1.201	11,579 B
EnvironmentTickCount	.NET Framework 4.8	1.5896 ns	0.0619 ns	0.0579 ns	0.027	13 B
EnvironmentTickCount64	.NET Framework 4.8	0.0000 ns	0.0000 ns	0.0000 ns	0.000	3 B
PInvokeTickCount64	.NET Framework 4.8	10.0051 ns	0.2299 ns	0.2038 ns	0.172	15 B
StopWatchGetElapsed	.NET Framework 4.8	25.6634 ns	0.5401 ns	0.6633 ns	0.444	171 B
StopWatchGetTimestamp	.NET Framework 4.8	23.4942 ns	0.3226 ns	0.3018 ns	0.404	117 B
DurationSinceEpoch	.NET Framework 4.8	10.2168 ns	0.2194 ns	0.1832 ns	0.176	15 B

[coveralls]

coverage: 99.318%. remained the same
when pulling aa3ca98 on users/alexpeck/winpinvoke
into a825808 on main.