Add GDScript .editorconfig rules

- Uniformize `.gd` unit test files indentation to tabs (where needed)

.editorconfig

@@ -21,3 +21,13 @@ indent_size = 4
 [*.{yml,yaml}]
 indent_style = space
 indent_size = 2
+
+# GDScript unit test files
+[*.gd]
+indent_style = tab
+indent_size = 4
+insert_final_newline = true
+trim_trailing_whitespace = true
+
+[*.out]
+insert_final_newline = true

modules/gdscript/tests/scripts/analyzer/errors/enum_preload_unnamed_assign_to_named.gd

@@ -1,4 +1,5 @@
 enum MyEnum { VALUE_A, VALUE_B, VALUE_C = 42 }
+
 func test():
 	const P = preload("../features/enum_value_from_parent.gd")
 	var local_var: MyEnum

modules/gdscript/tests/scripts/analyzer/features/base_outer_resolution.gd

@@ -11,4 +11,3 @@ func test() -> void:
 	Extend.InnerClass.InnerInnerClass.test_a_b_c(A.new(), B.new(), C.new())
 	Extend.InnerClass.InnerInnerClass.test_enum(C.TestEnum.HELLO_WORLD)
 	Extend.InnerClass.InnerInnerClass.test_a_prime(A.APrime.new())
-