fix(input): underline should only be thicker if focused (#6152)

* Currently the underline of the input container is always `2px` thick if the input is invalid. As per specifications the underline should be `1dp/px` if not focused.

src/lib/input/input-container.scss

@@ -202,7 +202,7 @@ textarea.mat-input-element {
 
   .mat-input-ripple {
     position: absolute;
-    height: $mat-input-underline-height * 2;
+    height: $mat-input-underline-height;
     top: 0;
     left: 0;
     width: 100%;
@@ -211,6 +211,10 @@ textarea.mat-input-element {
     visibility: hidden;
     transition: background-color $swift-ease-in-duration $swift-ease-in-timing-function;
 
+    .mat-focused & {
+      height: $mat-input-underline-height * 2;
+    }
+
     .mat-focused &,
     .mat-input-invalid & {
       visibility: visible;