Allow unnecessary [In, Out] attributes on blittable arrays and report them as unneces...

Allow unnecessary [In, Out] attributes on blittable arrays and report them as unnecessary (#87774)

* Change our '[In, Out]' attribute handling to have a concept of 'unnecessary but not invalid' to enable us in the future to report a non-fatal diagnostic.

* WIP enable unnecessary diagnostic in LibraryImportGenerator'

* Hook up diagnostics and add tests for LibraryImportGenerator

* Hook up diagnostics for ComInterfaceGenerator as well

* Update XLF

* Don't reference the live LibraryImportGenerator when building .NET 7 assets. Use the inbox instead.

* PR feedback

* Fix merge