filter: Mark messages as read in -is:dm view.

We avoid doing the more complex composability here, since that's
potentially risky.

Fixes #25113.

web/src/filter.ts

@@ -1204,6 +1204,10 @@ export class Filter {
             return true;
         }
 
+        if (_.isEqual(term_types, ["not-is-dm"])) {
+            return true;
+        }
+
         if (_.isEqual(term_types, ["is-resolved"])) {
             return true;
         }

web/tests/filter.test.cjs

@@ -347,6 +347,21 @@ test("basics", () => {
     assert.ok(filter.can_show_next_unread_dm_conversation_button());
     assert.ok(!filter.has_exactly_channel_topic_operators());
 
+    terms = [{operator: "is", operand: "dm", negated: true}];
+    filter = new Filter(terms);
+    assert.ok(!filter.contains_only_private_messages());
+    assert.ok(filter.can_mark_messages_read());
+    assert.ok(filter.contains_no_partial_conversations());
+    assert.ok(!filter.has_operator("search"));
+    assert.ok(filter.can_apply_locally());
+    assert.ok(!filter.is_personal_filter());
+    assert.ok(!filter.is_conversation_view());
+    assert.ok(!filter.is_channel_view());
+    assert.ok(filter.may_contain_multiple_conversations());
+    assert.ok(!filter.can_show_next_unread_topic_conversation_button());
+    assert.ok(!filter.can_show_next_unread_dm_conversation_button());
+    assert.ok(!filter.has_exactly_channel_topic_operators());
+
     // "is:private" was renamed to "is:dm"
     terms = [{operator: "is", operand: "private"}];
     filter = new Filter(terms);