[Chore] Publish symbols from CI builds to internal symbol server (#4910)

* Publish symbols from CI builds to internal symbol server

Add MicroBuildArchiveSymbols@6 to both build pipelines so PDBs for the shipping assemblies are archived to the internal symbol server. SubmitToInternet is false, so symbols never reach the public MSDL.

- New publish-symbols-stage.yml + publish-symbols-upload.yml templates so the same staging/upload pair can be reused by both pipelines. They're split because the staging step must run before the test step (the test step's DebugType, if it differed from the build step's, would invalidate MSBuild's up-to-date check and rebuild Core with a new MVID; combined with GeneratePackageOnBuild=true, that would also overwrite the produced nupkg with a DLL whose MVID no longer matched the PDB we uploaded).

- Align the test step's DebugType with the build step's DebugType in both pipelines, so the test step doesn't trigger that rebuild.

- build-core-lib (per-commit preview builds): gate the upload to main, dev, dev-v5, and archives/* — the branches in the pipeline's trigger that produce shipping nupkgs.

- build-all-lib (v* tag-triggered release builds, all 6 packages): gate the upload to refs/tags/v*.

- Stage glob covers src/**/bin/Release/**/Microsoft.FluentUI.*.{dll,pdb} with src/Templates/** excluded (Templates.csproj has IncludeBuildOutput=false; its placeholder DLL doesn't ship).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Clarify wording in template comment

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

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Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>