Bug 1728897 - Update Wasm try-delegate semantics to match spec r=rhunt

The semantics of the try-delegate Wasm exception handling instruction
was recently changed in this spec discussion:

  https://github.com/WebAssembly/exception-handling/issues/176

This patch adjusts compilation and validation to match the new
semantics, which allows delegate to target any block.

Differential Revision: https://phabricator.services.mozilla.com/D124424