Updated the playground to allow a validator selection

- Defaults to the `ajv6` validator
- Updated `package*.json` to add `@rjsf/utils` and `@rjsf/validator-ajv6`
  - Also removed a bunch of unnecessary packages
  - Bumped a bunch of other packages to the latest minor and patch version
  - Bumped a few select packages to the latest major version
- Updated `.eslintrc` to switch from `babel-eslint` to `@babel/eslint-parser`
- Updated the `index.js` file to add a `validators` object containing the `AJV6` validator choice, passing it into `Playground`
- Updated the `app.js` file to get `shouldRender()` from `@rjsf/utils` instead of copying it from core
  - Also extracted `validators` from the props for `Playground`, storing `validator` in the state, initially set to `AJV6`
  - Added a `ValidatorSelector` component that is used to update the selected `validator` in state
  - Rendered a `ValidagtorSelector` just before the `CopyLink` component
  - Passed `validators[validator]` as the `validator` prop on `FormComponent`

packages/playground/.eslintrc

@@ -1,5 +1,5 @@
 {
-    "parser": "babel-eslint",
+    "parser": "@babel/eslint-parser",
     "rules": {
         "react/jsx-uses-react": 2,
         "react/jsx-uses-vars": 2,
@@ -26,11 +26,6 @@
         "node": true
     },
     "extends": "eslint:recommended",
-    "ecmaFeatures": {
-        "modules": true,
-        "jsx": true,
-        "experimentalObjectRestSpread": true
-    },
     "plugins": [
         "jsx-a11y",
         "react"

packages/playground/.npmrc

@@ -0,0 +1,2 @@
+# Use legacy peer deps to allow things to install with node 16
+legacy-peer-deps=true