Move builtin signals to enum (#2309)

* Move builtin signals to enum

* Fix annotations

tests/test_signals.py

@@ -1,5 +1,6 @@
 import asyncio
 
+from enum import Enum
 from inspect import isawaitable
 
 import pytest
@@ -50,6 +51,25 @@ def test_invalid_signal(app, signal):
             ...
 
 
+@pytest.mark.asyncio
+async def test_dispatch_signal_with_enum_event(app):
+    counter = 0
+
+    class FooEnum(Enum):
+        FOO_BAR_BAZ = "foo.bar.baz"
+
+    @app.signal(FooEnum.FOO_BAR_BAZ)
+    def sync_signal(*_):
+        nonlocal counter
+
+        counter += 1
+
+    app.signal_router.finalize()
+
+    await app.dispatch("foo.bar.baz")
+    assert counter == 1
+
+
 @pytest.mark.asyncio
 async def test_dispatch_signal_triggers_multiple_handlers(app):
     counter = 0