Update Studio and Studio Plugin to v0.21.0. (#360)

## Changes
- Studio's startup time is now considerably faster. This is due to an
improvement in the logic for parsing Component and Template files.
(#357)
- The Studio Plugin is now a direct, explicit dependency of Studio. That
means users only have to install `@yext/studio`. They don't need to
worry about manually installing `@yext/studio-plugin` as well. (#355)

packages/studio-plugin/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@yext/studio-plugin",
-  "version": "0.20.0",
+  "version": "0.21.0",
   "types": "./lib/index.d.ts",
   "main": "./lib/index.js",
   "type": "module",

packages/studio/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@yext/studio",
-  "version": "0.20.0",
+  "version": "0.21.0",
   "types": "./lib/types.d.ts",
   "type": "module",
   "bin": {
@@ -20,7 +20,7 @@
     "@minoru/react-dnd-treeview": "^3.4.1",
     "@restart/ui": "^1.5.2",
     "@vitejs/plugin-react": "^4.0.4",
-    "@yext/studio-plugin": "0.20.0",
+    "@yext/studio-plugin": "0.21.0",
     "autoprefixer": "^10.4.14",
     "cac": "^6.7.14",
     "classnames": "^2.3.2",