Autocompletion: rework argument options string literal completion

modules/gdscript/tests/scripts/completion/common/identifiers_in_call.gd

@@ -0,0 +1,18 @@
+extends "res://completion/class_a.notest.gd"
+
+signal test_signal_1(a)
+signal test_signal_2(a: int)
+
+var test_var_1
+var test_var_2: int
+
+func test_func_1(t):
+    pass
+
+func test_func_2(t: int) -> void:
+    pass
+
+func _init(test_parameter_1, test_parameter_2: String):
+    var local_test_var_1
+    var local_test_var_2: int
+    print(t➡)