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/Form/Input.vue

@@ -1,7 +1,6 @@
 <script>
-import darkModeMixin from 'widget/mixins/darkModeMixin';
+import { useDarkMode } from 'widget/composables/useDarkMode';
 export default {
-  mixins: [darkModeMixin],
   props: {
     label: {
       type: String,
@@ -28,20 +27,33 @@ export default {
       default: '',
     },
   },
+  setup() {
+    const { getThemeClass } = useDarkMode();
+    return { getThemeClass };
+  },
   computed: {
     labelClass() {
       return this.error
-        ? `text-red-400 ${this.$dm('text-black-800', 'dark:text-slate-50')}`
-        : `text-black-800 ${this.$dm('text-black-800', 'dark:text-slate-50')}`;
+        ? `text-red-400 ${this.getThemeClass(
+            'text-black-800',
+            'dark:text-slate-50'
+          )}`
+        : `text-black-800 ${this.getThemeClass(
+            'text-black-800',
+            'dark:text-slate-50'
+          )}`;
     },
     isInputDarkOrLightMode() {
-      return `${this.$dm('bg-white', 'dark:bg-slate-600')} ${this.$dm(
-        'text-slate-700',
-        'dark:text-slate-50'
-      )}`;
+      return `${this.getThemeClass(
+        'bg-white',
+        'dark:bg-slate-600'
+      )} ${this.getThemeClass('text-slate-700', 'dark:text-slate-50')}`;
     },
     inputBorderColor() {
-      return `${this.$dm('border-black-200', 'dark:border-black-500')}`;
+      return `${this.getThemeClass(
+        'border-black-200',
+        'dark:border-black-500'
+      )}`;
     },
     inputHasError() {
       return this.error