chore: Replace messageMixing with useMessage composable [CW-3475] (#9942)

# Pull Request Template

## Description

Replaces the messageMixin with the new useMessage composable

Fixes
https://linear.app/chatwoot/issue/CW-3475/rewrite-messagemixin-mixin-to-a-composable

## Type of change

Please delete options that are not relevant.

- [ ] Bug fix (non-breaking change which fixes an issue)
- [x] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality not to work as expected)
- [ ] This change requires a documentation update

app/javascript/widget/mixins/messageMixin.js

@@ -1,13 +0,0 @@
-export default {
-  computed: {
-    messageContentAttributes() {
-      const { content_attributes: attribute = {} } = this.message;
-      return attribute;
-    },
-    hasAttachments() {
-      return !!(
-        this.message.attachments && this.message.attachments.length > 0
-      );
-    },
-  },
-};