Autocompletion: rework argument options string literal completion

modules/gdscript/tests/scripts/completion/argument_options/string_literals/argument_options_inside_string_literal.cfg

@@ -0,0 +1,5 @@
+[output]
+include=[
+    {"insert_text": "\"property_of_a\""},
+    {"insert_text": "\"name\""},
+]

modules/gdscript/tests/scripts/completion/argument_options/string_literals/argument_options_inside_string_literal.gd

@@ -0,0 +1,8 @@
+extends Node
+
+const A = preload ("res://completion/class_a.notest.gd")
+
+func _ready() -> void:
+    var a := A.new()
+    var tween := get_tree().create_tween()
+    tween.tween_property(a, "➡")