fix invalid Uri error when running in a Single file application

[hahn-kev]

When publishing a Single file application we would get an error when trying to initlize Icu. This PR fixes that issue.

To test run the following in the TestHelper project

dotnet publish -r win-x64 --property:PublishSingleFile=true --framework net8.0

the resulting exe can be found in icu-dotnet\output\Release\TestHelper\net8.0\win-x64\publish, copy in the native ICU dlls to that folder and run that with the following (numbers being the icu version range)

 .\TestHelper.exe 70 72

before this PR you would get this exception:

Unhandled exception. System.TypeInitializationException: The type initializer for 'Icu.NativeMethods' threw an exception.
 ---> System.UriFormatException: Invalid URI: The URI is empty.
   at System.Uri.CreateThis(String uri, Boolean dontEscape, UriKind uriKind, UriCreationOptions& creationOptions)
   at System.Uri..ctor(String uriString)
   at Icu.NativeMethods.get_DirectoryOfThisAssembly() in C:\dev\icu-dotnet\source\icu.net\NativeMethods\NativeMethods.cs:line 175
   at Icu.NativeMethodsHelper.TryGetPathFromAssemblyDirectory() in C:\dev\icu-dotnet\source\icu.net\NativeMethods\NativeMethodsHelper.cs:line 145
   at Icu.NativeMethodsHelper.GetIcuVersionInfoForNetCoreOrWindows() in C:\dev\icu-dotnet\source\icu.net\NativeMethods\NativeMethodsHelper.cs:line 65
   at Icu.NativeMethods.ResetIcuVersionInfo() in C:\dev\icu-dotnet\source\icu.net\NativeMethods\NativeMethods.cs:line 466
   at Icu.NativeMethods..cctor() in C:\dev\icu-dotnet\source\icu.net\NativeMethods\NativeMethods.cs:line 73
   --- End of inner exception stack trace ---
   at Icu.NativeMethods.SetMinMaxIcuVersions(Int32 minVersion, Int32 maxVersion) in C:\dev\icu-dotnet\source\icu.net\NativeMethods\NativeMethods.cs:line 37
   at Icu.Wrapper.ConfineIcuVersions(Int32 minIcuVersion, Int32 maxIcuVersion) in C:\dev\icu-dotnet\source\icu.net\IcuWrapper.cs:line 81
   at Icu.Tests.TestHelper.Main(String[] args) in C:\dev\icu-dotnet\source\TestHelper\TestHelper.cs:line 40

this is because Assembly.Location returns an empty string. Per the warning, I'm using AppContext.BaseDirectory when location returns an empty string.

It would be nice to have an automated test for this, but doing that would require doing something similar to above where we publish a SingleFile project and run it, not sure if that's worth it.

[github-actions]

Test Results

       5 files  ±0     403 suites  ±0   6s ⏱️ -1s
   431 tests ±0     427 ✔️ ±0    4 💤 ±0  0 ❌ ±0 
2 193 runs  ±0  2 095 ✔️ ±0  98 💤 ±0  0 ❌ ±0 

Results for commit c39404e. ± Comparison against base commit 9bce747.

♻️ This comment has been updated with latest results.