Validate theme.json files against the JSON Schema (#221)

* Install AJV validator

* Add validate script

* Update validateSchema

* Add lint-staged for theme.json schemas

* Update filename to file

* Add pre-commit hook

* Fix lint-staged

* Add schema url to the error output

* Leave error schema as undefined when missing

* Add error exit code for invalid commands

* Rewrite for latest ajv

* Revert to ajv@6

* Support both draft-04 and draft-07

* Add colored JSON output

* Add variations and font collection validation

* Fix glob for running validation in lint-staged

.husky/pre-commit

@@ -0,0 +1,4 @@
+#!/usr/bin/env sh
+. "$(dirname -- "$0")/_/husky.sh"
+
+npx lint-staged

.lintstagedrc.json

@@ -0,0 +1,3 @@
+{
+	"{**/theme.json,**/styles/*.json,**/assets/fonts/*.json}": "node ./theme-utils.mjs validate-schema"
+}