Adding System.Runtime.CompilerServices.Unsafe.BitCast (#82917)

Adding System.Runtime.CompilerServices.Unsafe.BitCast (#82917)

* Adding System.Runtime.CompilerServices.Unsafe.BitCast

* Adding some basic intrinsic recognition for Unsafe.BitCast

* Use ClassLayout::AreCompatible as part of Unsafe.BitCast

* Fixup BitConverter to use Unsafe.BitCast

* Fixup Enum to use Unsafe.BitCast

* Ensure BitCast resolves the right generic type for toTypeHnd

* Use Unsafe.BitCast in places using the `*(TTo*)&tfrom` pattern

* Don't use BitCast in places the generic constraints disallows it

* Missing semicolon

* Don't use Unsafe.BitCast where it introduces additional generic instantiations

* Don't regress the files that are used for both netstandard and netcoreapp

* Responding to PR feedback

* Fix a typo in the bitcast tests