Implement process and instance isolation

[jamescrosswell]

Resolves #2033, Resolves #1067

• Errors when initializing Sentry twice with caching enabled #2033
• Offline caching should support concurrent process instances #1067
• Auto Session Tracking should only be enabled by default on Mobile until total process isolation is supported sentry-unity#264

Todo

We're seeing an error in some entirely unrelated code on Windows ARM64. This is happening for other PRs as well, so unrelated to this PR.

• GetRuntime_AllProperties failing on WinArm64 #4712

Interprocess Locking

This turns out to be surprisingly difficult.

Something like a named Mutex could be used for this. However Mutexes are thread affine so they need to be released on the same thread that acquired them. Other than setting aside a dedicated thread for the lifetime of the Hub, there's no easy way to make that work.

A named Semaphore would be another option, but these aren't supported on macOS.

In the end I went with the "lock file" solution that @lucas-zimerman suggested. Keeping a lock file specific to each cache directory and opening this with FileShare.None gives us a kind of file based named mutex that we can use to avoid having multiple instances of the Hub trying to process files from the same cache directory.

[codecov]

Codecov Report

❌ Patch coverage is 77.16049% with 37 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (version6@522f80e). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
src/Sentry/Internal/Http/CachingTransport.cs	70.73%	19 Missing and 5 partials ⚠️
src/Sentry/Internal/CacheDirectoryCoordinator.cs	81.96%	9 Missing and 2 partials ⚠️
src/Sentry/Internal/ReadOnlyFilesystem.cs	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             version6    #4498   +/-   ##
===========================================
  Coverage            ?   73.36%           
===========================================
  Files               ?      482           
  Lines               ?    17567           
  Branches            ?     3473           
===========================================
  Hits                ?    12888           
  Misses              ?     3826           
  Partials            ?      853           

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[bruno-garcia]

@sentry review