[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