chore: Replace darkmode mixin with useDarkMode composable [CW-3474] (#9949)

# Pull Request Template

## Description

Replaces darkModeMixin with the new useDarkMode composable and replaces
wll usages of mixin the the composable in components and pages

Fixes
https://linear.app/chatwoot/issue/CW-3474/rewrite-darkmodemixin-mixin-to-a-composable

## Type of change

Please delete options that are not relevant.

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

---------

Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>
Co-authored-by: Sivin Varghese <64252451+iamsivin@users.noreply.github.com>

app/javascript/widget/components/template/EmailInput.vue

@@ -6,14 +6,13 @@ import { getContrastingTextColor } from '@chatwoot/utils';
 
 import FluentIcon from 'shared/components/FluentIcon/Index.vue';
 import Spinner from 'shared/components/Spinner.vue';
-import darkModeMixin from 'widget/mixins/darkModeMixin.js';
+import { useDarkMode } from 'widget/composables/useDarkMode';
 
 export default {
   components: {
     FluentIcon,
     Spinner,
   },
-  mixins: [darkModeMixin],
   props: {
     messageId: {
       type: Number,
@@ -25,7 +24,8 @@ export default {
     },
   },
   setup() {
-    return { v$: useVuelidate() };
+    const { getThemeClass } = useDarkMode();
+    return { v$: useVuelidate(), getThemeClass };
   },
   data() {
     return {
@@ -47,9 +47,9 @@ export default {
       );
     },
     inputColor() {
-      return `${this.$dm('bg-white', 'dark:bg-slate-600')}
-        ${this.$dm('text-black-900', 'dark:text-slate-50')}
-        ${this.$dm('border-black-200', 'dark:border-black-500')}`;
+      return `${this.getThemeClass('bg-white', 'dark:bg-slate-600')}
+        ${this.getThemeClass('text-black-900', 'dark:text-slate-50')}
+        ${this.getThemeClass('border-black-200', 'dark:border-black-500')}`;
     },
     inputHasError() {
       return this.v$.email.$error