[WebAssembly] Correctly check end_if/end_try with else/catch

When we encounter an `else`, `catch`, or `catch_all`, we currently just
push the structure `NestingType` and don't preserve the original `if`
and `try`'s signature. So after we pass `else`/`catch`/`catch_all`, we
can't check if the values on stack have the correct types when we
encounter `end_if` or `end_try`. This CL fixes the issue, and modifies
the existing test to be correct (some of them had `try` without
`catch`).

Reviewed By: dschuff

Differential Revision: https://reviews.llvm.org/D147881