rust-mode.el: `foo![...]` is not highlighted as macros.

[gifnksm]

foo![...] is one of a valid macro invocation syntax, but it is not highlighted correctly with emacs's rust-mode. Other invocation syntax foo!(...) and foo!{..} are highlighted correctly.

[gifnksm]

cc #8793

[huonw]

Closed by #14087 (via #14164).