Fix 4285 by adding support for MUI v6

- Updated `@rjsf/mui` to update the dev dependencies for `@mui/*` to v6 and the peer dependencies to add MUI v6
- Updated the playground to update `@mui/*` to v6
  - Also changed the dropdown name from `material-ui-5` to `mui` and switched `Layout` to use the `PropsWithChildren` for its props
  - Updated the `Form.test.tsx` to add information to the fake node to allow the tests to work with v6
  - Ran `npm run test:update` to update the snapshots due to the v6 and emotion upgrades
- Updated the test snapshots for `@rjsf/chakra-ui` which also uses emotion
- Updated `CHANGELOG.md` accordingly, bumping to `5.21.0`

Author: heath-freenome

CHANGELOG.md

@@ -16,19 +16,30 @@ should change the heading of the (upcoming) version to include a major version b
 
 -->
 
-# 5.20.2
+# 5.21.0
+
+## @rjsf/core
+
+- Updated `Form` to fix `focusOnError()` to support the ids that include dots, fixing [#4279](https://github.com/rjsf-team/react-jsonschema-form/issues/4279) 
+
+## @rjsf/mui
+
+- Updated the peer dependencies for `@mui/material` and `@mui/icon-material`, fixing [4283](https://github.com/rjsf-team/react-jsonschema-form/issues/4283)
 
 ## @rjsf/utils
 
 - Fixes an issue with dependencies computeDefaults to ensure we can get the dependencies defaults [#4271](https://github.com/rjsf-team/react-jsonschema-form/issues/4271)
 - Updated `deepEquals()` to use `fast-equals.createCustomEqual()` instead of `lodash.isEqualWith()`, fixing [#4291](https://github.com/rjsf-team/react-jsonschema-form/issues/4291)
   - Switched uses of `lodash.isEqual()` to `deepEquals()` in many of the utility functions as well
 
-
 ## @validator-ajv8
 
 - Use `@rjsf/utils` `deepEquals()` instead of `lodash.isEqual()` to improve performance, fixing [#4291](https://github.com/rjsf-team/react-jsonschema-form/issues/4291)
 
+## Dev / docs / playground
+
+- Updated the playground to use `@mui/*` version 6, changing the name of the dropdown from `material-ui-5` to `mui`
+
 # 5.20.1
 
 ## Dev / docs / playground