Rollup merge of #147771 - nxsaken:div_shlr_exact, r=dtolnay

Rename `*exact_{div,shr,shl}` to `*{div,shr,shl}_exact`

Related to rust-lang/rust#144336 and rust-lang/rust#139911, see rust-lang/rust#139911 (comment). I haven't touched the `exact_div`, `exact_udiv` and `exact_sdiv` intrinsics. Let me know if I should.

Author: Zalathar