Do not accept pattern_type from user input in push rules. (#15088)

Internally the push rules module uses a `pattern_type` property for `event_match`
conditions (and `related_event_match`) to mark the condition as matching the
current user's Matrix ID or localpart.

This is leaky to the Client-Server API where a user can successfully set a condition
which provides `pattern_type` instead of `pattern` (note that there's no benefit to
doing this -- the user can just use their own Matrix ID or localpart instead). When
serializing back to the client the `pattern_type` property is converted into a proper
`pattern`.

The following changes are made to avoid this:

* Separate the `KnownCondition::EventMatch` enum value into `EventMatch`
  and `EventMatchType`, each with their own expected properties. (Note that a
  similar change is made for `RelatedEventMatch`.)
* Make it such that the `pattern_type` variants serialize to the same condition kind,
  but cannot be deserialized (since they're only provided by base rules).
* As a final tweak, convert `user_id` vs. `user_localpart` values into an enum.

Author: clokep

changelog.d/15088.bugfix

@@ -0,0 +1 @@
+Fix a long-standing bug where Synapse handled an unspecced field on push rules.

rust/benches/evaluator.rs

@@ -60,8 +60,7 @@ fn bench_match_exact(b: &mut Bencher) {
     let condition = Condition::Known(synapse::push::KnownCondition::EventMatch(
         EventMatchCondition {
             key: "room_id".into(),
-            pattern: Some("!room:server".into()),
-            pattern_type: None,
+            pattern: "!room:server".into(),
         },
     ));
 
@@ -109,8 +108,7 @@ fn bench_match_word(b: &mut Bencher) {
     let condition = Condition::Known(synapse::push::KnownCondition::EventMatch(
         EventMatchCondition {
             key: "content.body".into(),
-            pattern: Some("test".into()),
-            pattern_type: None,
+            pattern: "test".into(),
         },
     ));
 
@@ -158,8 +156,7 @@ fn bench_match_word_miss(b: &mut Bencher) {
     let condition = Condition::Known(synapse::push::KnownCondition::EventMatch(
         EventMatchCondition {
             key: "content.body".into(),
-            pattern: Some("foobar".into()),
-            pattern_type: None,
+            pattern: "foobar".into(),
         },
     ));