Add fatal errors to memory vector size checks

[ashleynh]

I wonder if we should produce a fatal error here (and in similar places) so we don't forget to come back and fix it up later. @kripken, wdyt?

Originally posted by @tlively in https://github.com/WebAssembly/binaryen/pull/4811#discussion_r933629300

I agree that fatal errors are better in places like this.

Originally posted by @kripken in https://github.com/WebAssembly/binaryen/pull/4811#discussion_r946951478