Auto merge of #82565 - m-ou-se:ununstabilize-bits, r=kennytm

Revert reverting of stabilizing integer::BITS.

Now that `lexical-core` has an updated version that won't break with this stabilization, let's try to stabilize this again.

See https://github.com/rust-lang/rust/issues/81654#issuecomment-778564715

Tracking issue with FCP: https://github.com/rust-lang/rust/issues/76904

compiler/rustc_data_structures/src/lib.rs

@@ -13,7 +13,6 @@
 #![feature(unboxed_closures)]
 #![feature(generator_trait)]
 #![feature(fn_traits)]
-#![feature(int_bits_const)]
 #![feature(min_specialization)]
 #![feature(auto_traits)]
 #![feature(nll)]

compiler/rustc_serialize/src/lib.rs

@@ -16,7 +16,6 @@ Core encoding and decoding interfaces.
 #![feature(min_specialization)]
 #![feature(vec_spare_capacity)]
 #![feature(core_intrinsics)]
-#![feature(int_bits_const)]
 #![feature(maybe_uninit_array_assume_init)]
 #![feature(maybe_uninit_uninit_array)]
 #![feature(maybe_uninit_slice)]

compiler/rustc_serialize/tests/leb128.rs

@@ -1,4 +1,3 @@
-#![feature(int_bits_const)]
 #![feature(maybe_uninit_slice)]
 #![feature(maybe_uninit_uninit_array)]