KCheckbox: Remove local state management, rely on given props

KCheckbox had local data which are initialized to the given props for
`indeterminate` and `checked` and then updated in a watcher. This
resulted in that clicking a checkbox would always toggle it's
`isCurrentlyChecked` value and setting `isCurrentlyIndeterminate` to
false.

The changes here instead have KCheckbox simply use the given prop values
and does nothing to manage any internal state around whether it shows
`indeterminate` and/or `checked`.

This results in users of KCheckbox needing to be mindful of how they
manage the values they pass into KCheckbox's props as the component will
now reflect their values at all time.

lib/KCheckbox.vue

@@ -14,8 +14,8 @@
           type="checkbox"
           class="k-checkbox-input"
           :aria-checked="ariaChecked"
-          :checked="isCurrentlyChecked"
-          :indeterminate.prop="isCurrentlyIndeterminate"
+          :checked="checked"
+          :indeterminate.prop="indeterminate"
           :disabled="disabled"
           @click.stop="toggleCheck"
           @focus="isActive = true"
@@ -24,13 +24,13 @@
         >
 
         <KIcon
-          v-if="isCurrentlyIndeterminate"
+          v-if="indeterminate"
           :style="notBlank"
           class="checkbox-icon"
           icon="indeterminateCheck"
         />
         <KIcon
-          v-else-if="!isCurrentlyIndeterminate && isCurrentlyChecked"
+          v-else-if="!indeterminate && checked"
           :style="[ notBlank, activeOutline ]"
           class="checkbox-icon"
           icon="checked"
@@ -122,13 +122,11 @@
       },
     },
     data: () => ({
-      isCurrentlyChecked: false,
-      isCurrentlyIndeterminate: false,
       isActive: false,
     }),
     computed: {
       ariaChecked() {
-        return this.isCurrentlyIndeterminate ? 'mixed' : this.isCurrentlyChecked ? 'true' : 'false';
+        return this.indeterminate ? 'mixed' : this.checked ? 'true' : 'false';
       },
       id() {
         return `k-checkbox-${this._uid}`;
@@ -152,28 +150,14 @@
         };
       },
     },
-    watch: {
-      checked(newCheckedState) {
-        this.isCurrentlyChecked = newCheckedState;
-      },
-      indeterminate(newIndeterminateState) {
-        this.isCurrentlyIndeterminate = newIndeterminateState;
-      },
-    },
-    created() {
-      this.isCurrentlyChecked = this.checked;
-      this.isCurrentlyIndeterminate = this.indeterminate;
-    },
     methods: {
       toggleCheck(event) {
         if (!this.disabled) {
-          this.isCurrentlyChecked = !this.isCurrentlyChecked;
           this.$refs.kCheckboxInput.focus();
-          this.isCurrentlyIndeterminate = false;
           /**
            * Emits change event
            */
-          this.$emit('change', this.isCurrentlyChecked, event);
+          this.$emit('change', !this.checked, event);
         }
       },
       markInactive() {