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/composables/useMessage.js

@@ -0,0 +1,22 @@
+import { computed } from 'vue';
+
+/**
+ * Composable for handling message-related computations.
+ * @param {Object} message - The message object to be processed.
+ * @returns {Object} An object containing computed properties for message content and attachments.
+ */
+export function useMessage(message) {
+  const messageContentAttributes = computed(() => {
+    const { content_attributes: attribute = {} } = message;
+    return attribute;
+  });
+
+  const hasAttachments = computed(() => {
+    return !!(message.attachments && message.attachments.length > 0);
+  });
+
+  return {
+    messageContentAttributes,
+    hasAttachments,
+  };
+}