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/_forms.scss

@@ -11,6 +11,7 @@
   // height: $input-height;
   padding: $input-padding-y $input-padding-x;
   font-size: $font-size-base;
+  line-height: $input-line-height;
   color: $input-color;
   background-color: $input-bg;
   // Reset unusual Firefox-on-Android default style; see https://github.com/necolas/normalize.css/issues/214.