Auto merge of #52445 - alexcrichton:wasm-import-module, r=eddyb

Auto merge of #52445 - alexcrichton:wasm-import-module, r=eddyb

rustc: Stabilize #[wasm_import_module] as #[link(...)]

This commit stabilizes the `#[wasm_import_module]` attribute as
`#[link(wasm_import_module = "...")]`. Tracked by #52090 this new directive in
the `#[link]` attribute is used to configured the module name that the imports
are listed with. The WebAssembly specification indicates two utf-8 names are
associated with all imported items, one for the module the item comes from and
one for the item itself. The item itself is configurable in Rust via its
identifier or `#[link_name = "..."]`, but the module name was previously not
configurable and defaulted to `"env"`. This commit ensures that this is also
configurable.

Closes #52090