Feat: Add VariablePickerMenuPlugin to select variables in the prompt text box by menu #4764 (#4765)

### What problem does this PR solve?

Feat: Add VariablePickerMenuPlugin to select variables in the prompt
text box by menu #4764

### Type of change


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

web/src/components/prompt-editor/theme.ts

@@ -0,0 +1,43 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ */
+
+export default {
+  code: 'editor-code',
+  heading: {
+    h1: 'editor-heading-h1',
+    h2: 'editor-heading-h2',
+    h3: 'editor-heading-h3',
+    h4: 'editor-heading-h4',
+    h5: 'editor-heading-h5',
+  },
+  image: 'editor-image',
+  link: 'editor-link',
+  list: {
+    listitem: 'editor-listitem',
+    nested: {
+      listitem: 'editor-nested-listitem',
+    },
+    ol: 'editor-list-ol',
+    ul: 'editor-list-ul',
+  },
+  ltr: 'ltr',
+  paragraph: 'editor-paragraph',
+  placeholder: 'editor-placeholder',
+  quote: 'editor-quote',
+  rtl: 'rtl',
+  text: {
+    bold: 'editor-text-bold',
+    code: 'editor-text-code',
+    hashtag: 'editor-text-hashtag',
+    italic: 'editor-text-italic',
+    overflowed: 'editor-text-overflowed',
+    strikethrough: 'editor-text-strikethrough',
+    underline: 'editor-text-underline',
+    underlineStrikethrough: 'editor-text-underlineStrikethrough',
+  },
+};