Rollup merge of rust-lang#46870 - ffflorian:fix/slice/typo, r=rkruppe

docs(slice): Clarification in binary_search_by

This PR ~fixes a small comment typo~ adds some clarification to a half-open interval in the `binary_search_by` function in `slice`.

src/libcore/slice/mod.rs

@@ -400,7 +400,7 @@ impl<T> SliceExt for [T] {
         while size > 1 {
             let half = size / 2;
             let mid = base + half;
-            // mid is always in [0, size).
+            // mid is always in [0, size), that means mid is >= 0 and < size.
             // mid >= 0: by definition
             // mid < size: mid = size / 2 + size / 4 + size / 8 ...
             let cmp = f(unsafe { s.get_unchecked(mid) });