[clang] Implement CFG construction for @try and @catch

@finally is still not implemented.

With this, clang can emit -Wreturn-type warnings for functions containing
@try/@catch (but not yet @finally), and -Wunreachable-code also works for those
functions.

The implementation is similar to D36914.

Part of PR46693.

Differential Revision: https://reviews.llvm.org/D112287