Implement feature isolate_most_least_significant_one for integer types

[okaneco]

Accepted ACP - rust-lang/libs-team#467
Tracking issue - #136909

Implement ACP for functions that isolate the most significant set bit and least significant set bit on unsigned, signed, and NonZero integers.

Add function isolate_most_significant_one
Add function isolate_least_significant_one

---

This PR adds the following impls

impl {u8, u16, u32, u64, u128, usize} {
    const fn isolate_most_significant_one(self) -> Self;
    const fn isolate_least_significant_one(self) -> Self;
}
impl {i8, i16, i32, i64, i128, isize} {
    const fn isolate_most_significant_one(self) -> Self;
    const fn isolate_least_significant_one(self) -> Self;
}
impl NonZeroT {
    const fn isolate_most_significant_one(self) -> Self;
    const fn isolate_least_significant_one(self) -> Self;
}

Example behavior

assert_eq!(u8::isolate_most_significant_one(0b01100100), 0b01000000);
assert_eq!(u8::isolate_least_significant_one(0b01100100), 0b00000100);

[rustbot]

r? @thomcc

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[thomcc]

Mind implementing some tests?

[okaneco]

I wasn't sure of what kinds of tests to add.

Added tests for ints, uints, and NonZero which start with -1 or u*::MAX, then left/right shift appropriately to test each position for the most significant or least significant one.

// Right shift each loop
Bits         : 0b1111 | 0b0111 | 0b0011 | 0b0001
Most Sig One : 0b1000 | 0b0100 | 0b0010 | 0b0001
// Left shift each loop
Bits         : 0b1111 | 0b1110 | 0b1100 | 0b1000
Least Sig One: 0b0001 | 0b0010 | 0b0100 | 0b1000

Diff
https://github.com/rust-lang/rust/compare/03d89a1198e03333f7057edbd973eac89e167af2..97bc99a18f8175bf251a902fe5956e4d42fecebb

@rustbot label -S-waiting-on-author +S-waiting-on-review

[thomcc]

Thanks!

@bors r+

[bors]

📌 Commit 97bc99a has been approved by thomcc

It is now in the queue for this repository.