feat(checkbox): Updated cssClasses constant of checkbox (#4674)

Author: 태재영

packages/mdc-checkbox/constants.ts

@@ -28,9 +28,15 @@ export const cssClasses = {
   ANIM_INDETERMINATE_UNCHECKED: 'mdc-checkbox--anim-indeterminate-unchecked',
   ANIM_UNCHECKED_CHECKED: 'mdc-checkbox--anim-unchecked-checked',
   ANIM_UNCHECKED_INDETERMINATE: 'mdc-checkbox--anim-unchecked-indeterminate',
+  BACKGROUND: 'mdc-checkbox__background',
   CHECKED: 'mdc-checkbox--checked',
+  CHECKMARK: 'mdc-checkbox__checkmark',
+  CHECKMARK_PATH: 'mdc-checkbox__checkmark-path',
   DISABLED: 'mdc-checkbox--disabled',
   INDETERMINATE: 'mdc-checkbox--indeterminate',
+  MIXEDMARK: 'mdc-checkbox__mixedmark',
+  NATIVE_CONTROL: 'mdc-checkbox__native-control',
+  ROOT: 'mdc-checkbox',
   SELECTED: 'mdc-checkbox--selected',
   UPGRADED: 'mdc-checkbox--upgraded',
 };