Reconcile dotnet-api-docs descriptions with dotnet/runtime ///

[gewarren]

1. Generate IntelliSense XML files for each namespace in dotnet/runtime (see instructions below) - use a specific tag so all APIs already exist in dotnet-api-docs.
2. Copy the IntelliSense XML files to a branch in the binaries repo.
3. Consider (temporarily) reformatting all the ECMAXML files if this generates less noise in the IntelliSense files.
   • CLI: find . -name "*.xml" -type f | xargs -I'{}' xmllint --output '{}' --format '{}' (but this tool might do unwanted things)
   • VS Code extension (Red Hat XML) with xml.format.maxlinewidth set to 0 (disable) - sample PR is here.
4. Use the doc comment resolver tool in dotnet/docs-tools to update the IntelliSense files with any conflicting text from the dotnet-api-docs repo.
5. Open each file that was modified and resolve all the conflicts.
6. Run the CI pipeline to import the doc comments.
7. Use https://github.com/dotnet/api-docs-sync/tree/main/src/PortToTripleSlash to port the comments back to ///.
8. Open PRs in the dotnet/runtime repo.

Related items:

dotnet/runtime#44969
User Story 633174: [.NET] Partially import doc comments - Boards (azure.com)

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Associated WorkItem - 97017