Expose `no-modules` mode global variable name as a customizable command line flag

[crlf0710]

Currently this variable is using fixed string wasm_bindgen. Maybe it's better to expose this as a customizable flag.

[jesseditson]

This is available as the --no-modules-global flag!

[jesseditson]

Although upon testing it appears that the types do not get named properly if this is used, so there's likely at least a task around aligning those.