Fix ksp crash on unknown annotation (#290)

* Don't throw on unknown annotations

* Cleanup import

Author: chippmann

kt/entry-generation/godot-entry-generator/src/main/kotlin/godot/entrygenerator/model/GodotAnnotation.kt

@@ -1,5 +1,3 @@
 package godot.entrygenerator.model
 
-import godot.entrygenerator.model.GodotJvmSourceElement
-
 sealed interface GodotAnnotation : GodotJvmSourceElement

kt/entry-generation/godot-kotlin-symbol-processor/src/main/kotlin/godot/annotation/processor/ext/ksAnnotationExt.kt

@@ -215,8 +215,6 @@ fun KSAnnotation.mapToAnnotation(parentDeclaration: KSDeclaration): GodotAnnotat
                 global
             )
         }
-        else -> throw IllegalArgumentException(
-            "Unknown annotation: ${this.fqNameUnsafe}"
-        )
+        else -> null
     }
 }