fix(NcActions): use new slots api

- Since Vue 2.6 with new slots api, it is guaranteed that $scopedSlots has render function
  for all slots passed any way, while $slots only has value when using deprecated API or short-hand syntax
- It also closer to Vue 3 API
- `before` method is removed, there is no such lifecycle hook

Signed-off-by: Grigorii K. Shartsev <[email protected]>

src/mixins/actionGlobal.js

@@ -19,19 +19,7 @@
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  *
  */
-import Vue from 'vue'
-
 export default {
-	before() {
-		// all actions requires a valid text content
-		// if none, forbid the component mount and throw error
-		if (!this.$slots.default || this.text.trim() === '') {
-			Vue.util.warn(`${this.$options.name} cannot be empty and requires a meaningful text content`, this)
-			this.$destroy()
-			this.$el.remove()
-		}
-	},
-
 	beforeUpdate() {
 		this.text = this.getText()
 	},
@@ -52,7 +40,7 @@ export default {
 
 	methods: {
 		getText() {
-			return this.$slots.default ? this.$slots.default[0].text.trim() : ''
+			return this.$scopedSlots.default ? this.$scopedSlots.default()?.[0].text.trim() : ''
 		},
 	},
 }