updated button/form-control padding and line-height

- Moves from no set line-height (inherited of 1.5) to declared 1.25 for
all inputs and buttons (regardless of size modifier).

- Updates padding to be `.5rem` instead of `.375rem` so that padding is
more likely to be whole numbers based on the root font-size.

- Whole numbers will be beneficial in avoiding odd fractional pixels
that can lead to misalignment as shown in #18607.

- Large buttons and inputs are now a tad wider, and smaller
buttons/inputs a tad shorter and narrower, too.

scss/_buttons.scss

@@ -7,6 +7,7 @@
 .btn {
   display: inline-block;
   font-weight: $btn-font-weight;
+  line-height: $btn-line-height;
   text-align: center;
   white-space: nowrap;
   vertical-align: middle;