(core) Enable Record Cards

Summary:
Adds remaining functionality, fixes, and polish to Record Cards and
removes their feature flag, enabling them by default.

Test Plan: Tests deferred; will be included in a follow-up diff.

Reviewers: jarek, paulfitz

Reviewed By: jarek

Subscribers: paulfitz, jarek

Differential Revision: https://phab.getgrist.com/D4121

app/client/models/features.ts

@@ -33,7 +33,3 @@ export function PERMITTED_CUSTOM_WIDGETS(): Observable<string[]> {
   }
   return G.window.PERMITTED_CUSTOM_WIDGETS;
 }
-
-export function RECORD_CARDS() {
-  return Boolean(getGristConfig().experimentalPlugins);
-}