chore: Repalce message formatter mixin with useMessageFormatter [CW-3470] (#9986)

# Pull Request Template

## Description

Replaced the old messageFormatterMixin with a useMessageFormatter
composable

app/javascript/shared/mixins/messageFormatterMixin.js

@@ -1,40 +0,0 @@
-import MessageFormatter from '../helpers/MessageFormatter';
-
-export default {
-  methods: {
-    formatMessage(message, isATweet, isAPrivateNote) {
-      const messageFormatter = new MessageFormatter(
-        message,
-        isATweet,
-        isAPrivateNote
-      );
-      return messageFormatter.formattedMessage;
-    },
-    getPlainText(message, isATweet) {
-      const messageFormatter = new MessageFormatter(message, isATweet);
-      return messageFormatter.plainText;
-    },
-    truncateMessage(description = '') {
-      if (description.length < 100) {
-        return description;
-      }
-
-      return `${description.slice(0, 97)}...`;
-    },
-
-    highlightContent(content = '', searchTerm = '', highlightClass = '') {
-      const plainTextContent = this.getPlainText(content);
-
-      // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions#escaping
-      const escapedSearchTerm = searchTerm.replace(
-        /[.*+?^${}()|[\]\\]/g,
-        '\\$&'
-      );
-
-      return plainTextContent.replace(
-        new RegExp(`(${escapedSearchTerm})`, 'ig'),
-        `<span class="${highlightClass}">$1</span>`
-      );
-    },
-  },
-};

app/javascript/shared/mixins/specs/messageFormatterMixin.spec.js

@@ -1,17 +0,0 @@
-import { shallowMount } from '@vue/test-utils';
-import messageFormatterMixin from '../messageFormatterMixin';
-
-describe('messageFormatterMixin', () => {
-  it('returns correct plain text', () => {
-    const Component = {
-      render() {},
-      mixins: [messageFormatterMixin],
-    };
-    const wrapper = shallowMount(Component);
-    const message =
-      '<b>Chatwoot is an opensource tool. https://www.chatwoot.com</b>';
-    expect(wrapper.vm.getPlainText(message)).toMatch(
-      'Chatwoot is an opensource tool. https://www.chatwoot.com'
-    );
-  });
-});