We need to add tests for this special case, and make sure that the compiler rejects it as a usesite error (if the attribute doesn't exist, then there is a problem with IL and this symbol should not be used).

Testing should cover:

• method parameters
• method return types
• properties
• indexers parameters
• indexers return types
• delegates parameters
• delegates return types

Look for tests starting InAttributeModReqIsConsumedInRefCustomModifiersPosition_IL as a guide.

Found in #19658