Use global packages cache for local builds by default in CoreC… (dotnet/coreclr#27373)

Use global packages cache for local builds by default in CoreC… (dotnet/coreclr#27373)

* Get the product build to use the global package cache only.

* Move external.csproj out to the tests folder. Fix restore location so external.csproj correctly resolves its nuget-generated props/targets files.

* Fix typo.

* Fix expected failure case on platforms that don't support PGO/IBC.

* Don't error out if optimization data is not supported for the current platform.

* Fix casing that was causing the Linux x64 build to fail to find the pgo/ibc packages.

* Fix condition.

* Pass OS-Arch-Config to external test package restore.

* The platform-specific version of Microsoft.NETCore.CoreDisTools is an older version for non-Windows, so hardcode that version in stress_dependencies.csproj

Commit migrated from https://github.com/dotnet/coreclr/commit/f0887c4aea35f503dd212f0dab997f79d9f96f85