runtime: InMemoryDirectoryInfo is unexpectedly dependent on working directory due to its use of GetFullPath.

From the runtime-coreclr libraries-jitstress pipeline:

https://dev.azure.com/dnceng/public/_build/results?buildId=1069450&view=ms.vss-test-web.build-test-results-tab

This test fails all Windows arm64 runs (including JITMinOpts=1), with:

COMPlus_JITMinOpts=1
COMPlus_TieredCompilation=0

D:\h\w\BAA10A61\w\A0300974\e>call RunTests.cmd --runtime-path D:\h\w\BAA10A61\p 
----- start Fri 04/02/2021  1:01:32.06 ===============  To repro directly: ===================================================== 
pushd D:\h\w\BAA10A61\w\A0300974\e\
"D:\h\w\BAA10A61\p\dotnet.exe" exec --runtimeconfig Microsoft.Extensions.FileSystemGlobbing.Tests.runtimeconfig.json --depsfile Microsoft.Extensions.FileSystemGlobbing.Tests.deps.json xunit.console.dll Microsoft.Extensions.FileSystemGlobbing.Tests.dll -xml testResults.xml -nologo -nocolor -notrait category=IgnoreForCI -notrait category=OuterLoop -notrait category=failing 
popd
===========================================================================================================

D:\h\w\BAA10A61\w\A0300974\e>"D:\h\w\BAA10A61\p\dotnet.exe" exec --runtimeconfig Microsoft.Extensions.FileSystemGlobbing.Tests.runtimeconfig.json --depsfile Microsoft.Extensions.FileSystemGlobbing.Tests.deps.json xunit.console.dll Microsoft.Extensions.FileSystemGlobbing.Tests.dll -xml testResults.xml -nologo -nocolor -notrait category=IgnoreForCI -notrait category=OuterLoop -notrait category=failing  
  Discovering: Microsoft.Extensions.FileSystemGlobbing.Tests (method display = ClassAndMethod, method display options = None)
  Discovered:  Microsoft.Extensions.FileSystemGlobbing.Tests (found 97 test cases)
  Starting:    Microsoft.Extensions.FileSystemGlobbing.Tests (parallel test collections = on, max threads = 8)
    Microsoft.Extensions.FileSystemGlobbing.Tests.FunctionalTests.VerifyInMemoryDirectoryInfo_IsNotEmpty [FAIL]
      Assert.Equal() Failure
      Expected: 1
      Actual:   0
      Stack Trace:
        /_/src/libraries/Microsoft.Extensions.FileSystemGlobbing/tests/FunctionalTests.cs(858,0): at Microsoft.Extensions.FileSystemGlobbing.Tests.FunctionalTests.VerifyInMemoryDirectoryInfo_IsNotEmpty()
  Finished:    Microsoft.Extensions.FileSystemGlobbing.Tests
=== TEST EXECUTION SUMMARY ===
   Microsoft.Extensions.FileSystemGlobbing.Tests  Total: 343, Errors: 0, Failed: 1, Skipped: 0, Time: 7.984s
----- end Fri 04/02/2021  1:01:42.74 ----- exit code 1 ----------------------------------------------------------