Add tests for marshalling as VARIANT_BOOL or VARIANT (#20856)

Add tests for marshalling as VARIANT_BOOL or VARIANT (#20856)

* Add native side impl for VARIANT_BOOL test.

* More bool native code.

* Add VariantBool marshalling tests.

* Add infrastructure for tests for object -> VARIANT marshalling.

* Add variant tests for all built-in types.

* Clean up Variant tests.

* Add test for passing custom structure as object.

* Add test for VARIANT_BOOL byref.

* Added byref tests for VARIANT marshalling.

* Add field marshalling tests for VARIANT.

* Move ByValue tests to not have two sources of truth.

* Make managed code the one source of truth.

* Clean up formatting/unused methods.

* Clean up some whitespace issues.

* Add tests for BStrWrapper and CurrencyWrapper marshalling.

* Add UnknownWrapper tests.

* Add a test for VariantWrapper and PInvoke.

* PR Feedback.

* Remove ToString.

* Fix visibility

* Fix MSBuild import path.

* Clean up Variant tests.