Add tests, remove unused code, fix bugs

- Added tests for more error messages
- Test the "go to reference" feature at every character index of every
test case
- Delete unused code and imports
- Fix some bugs I found along the way

blueprintcompiler/language/gobject_property.py

@@ -51,7 +51,7 @@ class Property(AstNode):
 
     @property
     def document_symbol(self) -> DocumentSymbol:
-        if isinstance(self.value, ObjectValue):
+        if isinstance(self.value, ObjectValue) or self.value is None:
             detail = None
         else:
             detail = self.value.range.text