[Matrix] Move C++ matrix cast checks to TryStaticCast.

At the moment, the matrix support in CheckCXXCStyleCast (added in
D101696) breaks function-style constructor calls that take a
single matrix value, because it is treated as matrix cast.

Instead, unify the C++ matrix cast handling by moving the logic to
TryStaticCast and only handle the case where both types are matrix
types. Otherwise, fall back to the generic mis-match detection.

Suggested by @rjmccall

Reviewed By: SaurabhJha

Differential Revision: https://reviews.llvm.org/D103163