Implement Text-Based Performance Log

[brianrob]

Implements a text-based performance log scheme that writes coarse-grained performance logs:

• No logs are written unless the user opts-in by setting DOTNET_CLI_PERF_LOG=1.
• Each log is represented on disk as a directory, containing a collection of log files. Each process involved in an invocation of the CLI writes its own log file. Thus, when new processes are spawned by the CLI, there can be more than one log file.
• Logs are written by default to <DotnetUserProfilePath>\PerformanceLogs. Logs for an individual invocation of the CLI can be redirected via DOTNET_PERFLOG_DIR.
• By default, the most recent 10 logs are kept. This is changeable via DOTNET_PERF_LOG_COUNT. Set this variable to -1 to keep all logs.
• Data in the logs are emitted via PerformanceLogEventSource so that the events can be consumed through other profilers, such as those that use ETW.
• Sets DOTNET_PERFLOG_DIR when spawning msbuild processes so that msbuild can contribute to the performance log.

cc: @marcpopMSFT, @davidfowl, @DamianEdwards, @bwadswor

[wli3]

@sfoslund @dsplaisted @joeloff FYI, I reviewed most of the PR in a fork wli3#1 already

[brianrob]

Confirmed that GlobalMemoryStatusEx works on nanoserver:

C:\dotnet>type c:\users\ContainerUser\.dotnet\PerformanceLogs\f1cb9ab6bd3f4268be1ff25cb9e6a8db\perf-8764-97a83818cc9c492
1bee3ffa80ac3d72a.log
...
[2020-11-03T19:35:13.3215336Z] Event=Microsoft-Dotnet-CLI-Performance/MemoryConfiguration ProcessID=8764 ThreadID=1
memoryLoad="36" availablePhysicalMB="5172" totalPhysicalMB="8191"
...

[wli3]

@brianrob good to merge

[brianrob]

Thanks @wli3!