[multibyte] Support offset and align for array load and store (#8923)

Add offset and alignment immediates to ArrayLoad and ArrayStore AST
nodes, text format, and binary encoding.

Multibyte array access operations in the WebAssembly GC spec reuse
memarg immediates to specify a static byte offset and alignment hint.
This adds support for parsing, printing, and binary reading/writing of
these attributes for array load and store instructions.