Auto merge of #137907 - compiler-errors:inline-fnonce, r=saethlin

Inline `FnOnce`/`FnMut`/`Fn` shims once again

This PR fixes the argument checking for `extern "rust-call"` ABI functions with a spread arg, which do no expect their arguments to be exploded from a tuple like closures do.

Secondly, it removes the hack that prevented them from being inlined. This results in more work done by the compiler, but it does end up allowing us to inline functions we didn't before.

Fixes #137901

Author: bors