Make signal delegate static to avoid memory allocation (#695)

* Make signal delegate static to avoid memory allocation

Author: CedNaru

docs/src/doc/user-guide/signals.md

@@ -9,7 +9,7 @@ To create a signal use the delegate function `signal` and annotate it with `@Reg
 @RegisterClass
 class RotatingCube: Node3D() {
     @RegisterSignal
-    val reverseChanged by signal<Boolean>("reverse")
+    val reverseChanged: Signal1<Boolean> by signal("reverse")
 }
 ```