Rollup merge of #58628 - RReverser:optimise-vec-false, r=oli-obk

Optimise vec![false; N] to zero-alloc

Nowadays booleans have a well-defined representation, so there is no reason not to optimise their allocation.

src/liballoc/vec.rs

@@ -1610,6 +1610,7 @@ fn is_zero(&self) -> bool {
 impl_is_zero!(u128, |x| x == 0);
 impl_is_zero!(usize, |x| x == 0);
 
+impl_is_zero!(bool, |x| x == false);
 impl_is_zero!(char, |x| x == '\0');
 
 impl_is_zero!(f32, |x: f32| x.to_bits() == 0);