Rollup merge of #103570 - lukas-code:stabilize-ilog, r=scottmcm

Rollup merge of #103570 - lukas-code:stabilize-ilog, r=scottmcm

Stabilize integer logarithms

Stabilizes feature `int_log`.

I've also made the functions const stable, because they don't depend on any unstable const features. `rustc_allow_const_fn_unstable` is just there for `Option::expect`, which could be replaced with a `match` and `panic!`. cc ``@rust-lang/wg-const-eval``

closes https://github.com/rust-lang/rust/issues/70887 (tracking issue)

~~blocked on FCP finishing: https://github.com/rust-lang/rust/issues/70887#issuecomment-1289028216~~
FCP finished: https://github.com/rust-lang/rust/issues/70887#issuecomment-1302121266