[WebAssembly] Support Wasm EH + Wasm SjLj

D108960 added support for SjLj using Wasm EH instructions, which we call
Wasm SjLj going forward. (We call the old SjLj Emscripten SjLj) But it
did not support using Wasm EH and Wasm SjLj together. So far users of
Wasm EH had to use Wasm EH with Emscripten SjLj, which had a certain
limitation and it suffered from bigger code size increases as well.

This enables using Wasm EH and Wasm SjLj together.
1. This redirects `catchswitch` and `cleanupret` that unwind to caller
   to `catch.dispatch.longjmp` BB, which is a `catchswitch` BB that
   handles longjmps.
2. D108960 converted all longjmpable `call`s to `invokes` that unwind to
   `catch.dispatch.longjmp`. This CL checks if the `call` is embedded
   within another `catchpad`, and if so, makes it unwind to its nearest
   parent's unwind destination, rather than `catch.dispatch.longjmp`.
   This is necessary to preserve the scoping structure.

Reviewed By: dschuff

Differential Revision: https://reviews.llvm.org/D117610