Fix ResXFileRef/Bitmap href paths in translated .resx/.vsct: relative instead of absolute

[Copilot]

TranslateSource was baking absolute paths into translated .resx and .vsct files written to the intermediate output directory. Any repo rename/move caused subsequent builds to fail with MSB3103: Could not find a part of the path 'C:\old-location\...' because the stale absolute paths no longer resolved.

Root cause

RewriteRelativePathsToAbsolute in ResxDocument and VsctDocument resolved ResXFileRef/Bitmap href paths against the source .resx/.vsct directory and stored them as absolute paths — making the cached output location-dependent.

Changes

• TranslatableDocument — replaces the old single-arg RewriteRelativePathsToAbsolute(sourceFullPath) with:

  • RewriteRelativePathsForOutputPath(sourceFullPath, outputFullPath) — new virtual method subclasses override
  • MakeRelativePath(fromDirectory, toPath) — protected static helper using Uri.MakeRelativeUri; falls back to absolute when source/output are on different drives

• ResxDocument — overrides RewriteRelativePathsForOutputPath; rewrites ResXFileRef value paths relative to the output .resx directory

• VsctDocument — same fix for <Bitmap href="..."> attributes

• TranslateSource — calls RewriteRelativePathsForOutputPath(sourcePath, translatedFullPath) instead of the old single-arg form

• Tests — updated ResxDocumentTests and VsctDocumentTests to assert the output contains a relative path and does not contain the absolute base path; covers the typical case where source and output directories differ

Before / after (intermediate MyProject.resx):

<!-- Before: breaks after repo rename -->
<value>C:\Users\me\repos\myproject\src\MyProject\Dictionary.dic;System.String</value>

<!-- After: survives repo rename/move -->
<value>..\..\..\src\MyProject\Dictionary.dic;System.String</value>

To double check:

• The right tests are in and the right validation has happened. Guidance: https://github.com/dotnet/arcade/blob/main/Documentation/Validation.md