Enable in tree runtime pack for all of mono

[steveisok]

After working with this in a mobile context, I can see it providing benefits to all of mono. Most notably as a replacement for our 'patch-dotnet' target.

• Relax the check for BinPlaceTestRuntimePack to be RuntimeFlavor = 'mono'
• For desktop, the test host needs to be generated, so ensure that's still working right (basically, you should successfully run libraries tests)
• Validate lib-runtime-packs folder is created w/ the right contents

[ghost]

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