When unconditionally casting from a base to a final derived class, e.g. `base as! Derived`, the program did not abort with a trap.
Instead the resulting null-pointer caused a crash later in the program.
This fix inserts a trap condition for the failing case of such a cast.
rdar://151462303
Pass the correct type to `emitHeapMetadataRefForHeapObject()`.
Fixes a runtime crash in case a class protocol is cast to a final swift class, where the actual object is an ObjectiveC class instance.
rdar://99626888
When casting a class instance to a final class, we can directly compare the isa-pointer with address of the metadata.
This avoids a call to `swift_dynamicCastClass`.
It also avoids a call to the metadata accessor of the class (which calls `swift_getInitializedObjCClass`).
For comparing the metadata pointers it's not required that the metadata is fully initialized.
