Use round/rounded focus helper for radio/checkbox (quasarframework#2200)

Author: pdanpdan

src/css/core/visibility.styl

@@ -110,6 +110,10 @@ for type in desktop mobile cordova electron ios mat touch within-iframe platform
   border-radius inherit
   opacity .15
   transition background-color .3s cubic-bezier(.25, .8, .5, 1)
+.q-focus-helper-rounded
+  border-radius $generic-border-radius
+.q-focus-helper-round
+  border-radius 50%
 
 body
   &.desktop

src/mixins/option.js

@@ -100,7 +100,10 @@ export default {
           on: { change: this.toggle }
         }),
         this.$q.platform.is.desktop
-          ? h('div', { staticClass: 'q-focus-helper' })
+          ? h('div', {
+            staticClass: 'q-focus-helper',
+            'class': this.__kebabTag === 'q-radio' ? 'q-focus-helper-round' : 'q-focus-helper-rounded'
+          })
           : null,
         this.__getContent(h)
       ]),