Implement MSC3952: intentional mentions (#3092)

* Add experimental push rules.

* Update for changes to MSC3952: Use event_property_is and event_property_contains.

* Revert custom user/room mention conditions.

* Skip legacy rule processing if mentions exist.

* Add client option for intentional mentions.

* Fix tests.

* Test leagcy behavior with intentional mentions.

* Handle simple review comments.

src/client.ts

@@ -461,6 +461,11 @@ export interface IStartClientOpts {
      * @experimental
      */
     slidingSync?: SlidingSync;
+
+    /**
+     * @experimental
+     */
+    intentionalMentions?: boolean;
 }
 
 export interface IStoredClientOpts extends IStartClientOpts {}
@@ -8575,7 +8580,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
      */
     public setPushRules(rules: IPushRules): void {
         // Fix-up defaults, if applicable.
-        this.pushRules = PushProcessor.rewriteDefaultRules(rules);
+        this.pushRules = PushProcessor.rewriteDefaultRules(rules, this.getUserId()!);
         // Pre-calculate any necessary caches.
         this.pushProcessor.updateCachedPushRuleKeys(this.pushRules);
     }
@@ -9472,6 +9477,15 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
         return this.clientOpts?.threadSupport || false;
     }
 
+    /**
+     * A helper to determine intentional mentions support
+     * @returns a boolean to determine if intentional mentions are enabled
+     * @experimental
+     */
+    public supportsIntentionalMentions(): boolean {
+        return this.clientOpts?.intentionalMentions || false;
+    }
+
     /**
      * Fetches the summary of a room as defined by an initial version of MSC3266 and implemented in Synapse
      * Proposed at https://github.com/matrix-org/matrix-doc/pull/3266