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/dashboard/components/CustomAttribute.vue

@@ -5,7 +5,7 @@ import { BUS_EVENTS } from 'shared/constants/busEvents';
 import MultiselectDropdown from 'shared/components/ui/MultiselectDropdown.vue';
 import HelperTextPopup from 'dashboard/components/ui/HelperTextPopup.vue';
 import { isValidURL } from '../helper/URLHelper';
-import customAttributeMixin from '../mixins/customAttributeMixin';
+import { getRegexp } from 'shared/helpers/Validators';
 import { useVuelidate } from '@vuelidate/core';
 
 const DATE_FORMAT = 'yyyy-MM-dd';
@@ -15,7 +15,6 @@ export default {
     MultiselectDropdown,
     HelperTextPopup,
   },
-  mixins: [customAttributeMixin],
   props: {
     label: { type: String, required: true },
     description: { type: String, default: '' },
@@ -128,8 +127,7 @@ export default {
         required,
         regexValidation: value => {
           return !(
-            this.attributeRegex &&
-            !this.getRegexp(this.attributeRegex).test(value)
+            this.attributeRegex && !getRegexp(this.attributeRegex).test(value)
           );
         },
       },