feat: Rewrite customAttributeMixin to validation helper (#9916)

# Pull Request Template

## Description

This PR will replace the use of `customAttributeMixin` with
`shared/helpers/Validators` helper.

Fixes
https://linear.app/chatwoot/issue/CW-3446/rewrite-customattributemixin-mixin-to-a-composable

**Files updated**
1. widget/components/PreChat/Form.vue
2. dashboard/components/CustomAttribute.vue
3. dashboard/routes/dashboard/settings/attributes/EditAttribute.vue

## Type of change

- [x] New feature (non-breaking change which adds functionality)

## How Has This Been Tested?

Test the custom validation is working or not with the custom attributes.


## Checklist:

- [x] My code follows the style guidelines of this project
- [x] I have performed a self-review of my code
- [x] I have commented on my code, particularly in hard-to-understand
areas
- [ ] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [x] I have added tests that prove my fix is effective or that my
feature works
- [x] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged and published in downstream
modules

app/javascript/widget/components/PreChat/Form.vue

@@ -3,25 +3,19 @@ import CustomButton from 'shared/components/Button.vue';
 import Spinner from 'shared/components/Spinner.vue';
 import { mapGetters } from 'vuex';
 import { getContrastingTextColor } from '@chatwoot/utils';
-import messageFormatterMixin from 'shared/mixins/messageFormatterMixin';
 import { isEmptyObject } from 'widget/helpers/utils';
+import { getRegexp } from 'shared/helpers/Validators';
+import messageFormatterMixin from 'shared/mixins/messageFormatterMixin';
 import routerMixin from 'widget/mixins/routerMixin';
 import darkModeMixin from 'widget/mixins/darkModeMixin';
 import configMixin from 'widget/mixins/configMixin';
-import customAttributeMixin from '../../../dashboard/mixins/customAttributeMixin';
 
 export default {
   components: {
     CustomButton,
     Spinner,
   },
-  mixins: [
-    routerMixin,
-    darkModeMixin,
-    messageFormatterMixin,
-    configMixin,
-    customAttributeMixin,
-  ],
+  mixins: [routerMixin, darkModeMixin, messageFormatterMixin, configMixin],
   props: {
     options: {
       type: Object,
@@ -184,7 +178,7 @@ export default {
       return this.formValues[name] || null;
     },
     getValidation({ type, name, field_type, regex_pattern }) {
-      let regex = regex_pattern ? this.getRegexp(regex_pattern) : null;
+      let regex = regex_pattern ? getRegexp(regex_pattern) : null;
       const validations = {
         emailAddress: 'email',
         phoneNumber: ['startsWithPlus', 'isValidPhoneNumber'],