Non-natural alignment should fail to validate for atomic instructions

[stevenfontanella]

See WebAssembly/threads#242 and http://github.com/WebAssembly/binaryen/pull/8961. Currently alignment is ignored and non-natural alignment passes validation.

[ANAMASGARD]

Hi @stevenfontanella I’ve raised PR #8966 to fix this issue . When you have some time, could you please take a look and review it? Thanks!