Add isModifierActive helper function to actions with modifier mask.

config-serializer/config-items/KeystrokeWithModifiersAction.ts

@@ -1,3 +1,5 @@
+import {KeyModifiers} from './KeystrokeModifiersAction';
+
 class KeystrokeWithModifiersAction extends KeyAction {
 
     // @assertUInt8
@@ -37,4 +39,8 @@ class KeystrokeWithModifiersAction extends KeyAction {
     toString(): string {
         return `<KeystrokeWithModifiersAction scancode="${this.scancode}" modifierMask="${this.modifierMask}">`;
     }
+
+    isModifierActive(modifier: KeyModifiers): boolean {
+        return (this.modifierMask & modifier) > 0;
+    }
 }