Fix incorrect path used to find bundled x64 runtimes on Arm64

[mrward]

The wrong runtimes were resolved for dotnet x64 on Arm64 machines. The FileSystemExplorer was using the dotnet Arm64 path /usr/local/share/dotnet to find the x64 runtimes, instead of the emulated dotnet install path.

[baronfel]

@joeloff does this line up with your expectation of the layouts for the runtimes on macOS?

[joeloff]

@joeloff does this line up with your expectation of the layouts for the runtimes on macOS?

Yes. though it would apply to the SDK too. Any x64 pieces should get installed under dotnet/x64 on arm64 if you installed using the pkg. When installing through a tar I think it's pretty much free-for-all