fix: inconsistent behavior with multiple invocations of SwaggerUI (via #4923)

* add narrow e2e tests
* add failing system unit test
* break plugin object inheritance in combinePlugins
* style: add braces to if block
* drop unused `lodash.repeat` import
* remove deep-freeze from lockfile

package.json

@@ -48,6 +48,7 @@
   "dependencies": {
     "@braintree/sanitize-url": "^2.0.2",
     "@kyleshockey/js-yaml": "^1.0.1",
+    "@kyleshockey/object-assign-deep": "^0.4.2",
     "base64-js": "^1.2.0",
     "classnames": "^2.2.5",
     "core-js": "^2.5.1",