(core) Implement much of the general AccessRules UI.

Summary:
- Factored out ACLRuleCollection into its own file, and use for building UI.
- Moved AccessRules out of UserManager to a page linked from left panel.
- Changed default RulePart to be the last part of a rule for simpler code.
- Implemented much of the UI for adding/deleting rules.
  - For now, editing the ACLFormula and Permissions is done using text inputs.
- Implemented saving rules by syncing a bundle of them.
- Fixed DocData to clean up action bundle in case of an early error.

Test Plan: WIP planning to add some new browser tests for the UI

Reviewers: paulfitz

Reviewed By: paulfitz

Differential Revision: https://phab.getgrist.com/D2678

app/common/gutil.ts

@@ -789,3 +789,13 @@ export async function isLongerThan(promise: Promise<any>, timeoutMsec: number):
 export function isAffirmative(parameter: any): boolean {
   return ['1', 'on', 'true', 'yes'].includes(String(parameter).toLowerCase());
 }
+
+/**
+ * Returns whether a value is neither null nor undefined, with a type guard for the return type.
+ *
+ * This is particularly useful for filtering, e.g. if `array` includes values of type
+ * T|null|undefined, then TypeScript can tell that `array.filter(isObject)` has the type T[].
+ */
+export function isObject<T>(value: T | null | undefined): value is T {
+  return value !== null && value !== undefined;
+}