fix(checkbox): label content should not wrap

* Similar as for the radio component, the checkbox label content should not wrap if it exceeds the boundaries of the parent element. This ensures that we have consistent behavior across all selection controls.
* Fixes that the radio container (circle) shrinks if the label content is exceeding the boundaries and wrapping is enabled (developers may overwrite CSS to enable wrapping)

Closes #6671

src/lib/checkbox/checkbox.scss

@@ -193,6 +193,7 @@ $_mat-checkbox-mark-stroke-size: 2 / 15 * $mat-checkbox-size !default;
   align-items: baseline;
   vertical-align: middle;
   display: inline-flex;
+  white-space: nowrap;
 }
 
 .mat-checkbox-inner-container {

src/lib/radio/radio.scss

@@ -24,9 +24,12 @@ $mat-radio-ripple-size: $mat-radio-size * 0.75;
 .mat-radio-container {
   box-sizing: border-box;
   display: inline-block;
-  height: $mat-radio-size;
   position: relative;
   width: $mat-radio-size;
+  height: $mat-radio-size;
+  // The radio container is inside of a inline-flex element and may shrink if the label
+  // is wide and text-wrapping is enabled.
+  flex-shrink: 0;
 }
 
 // The outer circle for the radio, always present.