fix(preview): uri-encode search params

This change applies basic URI encoding to knob keys/values in
`<iframe>` URL and torn-away window URL in preview.

Fixes storybookjs#11641.

examples/official-storybook/stories/addon-knobs/with-knobs.stories.js

@@ -374,3 +374,7 @@ export const WithDuplicateDecorator = () => {
   return text('Text', 'Hello');
 };
 WithDuplicateDecorator.decorators = [withKnobs];
+
+export const WithKnobValueToBeEncoded = () => {
+  return text('Text', '10% 20%');
+};

lib/ui/src/components/preview/utils/stringifyQueryParams.tsx

@@ -1,2 +1,5 @@
 export const stringifyQueryParams = (queryParams: Record<string, string>) =>
-  Object.entries(queryParams).reduce((acc, [k, v]) => `${acc}&${k}=${v}`, '');
+  Object.entries(queryParams).reduce(
+    (acc, [k, v]) => `${acc}&${encodeURIComponent(k)}=${encodeURIComponent(v)}`,
+    ''
+  );