GDScript: Fix missing conversion for default argument values

modules/gdscript/tests/scripts/runtime/features/conversion_for_default_parameter.gd

@@ -0,0 +1,19 @@
+func literal(x: float = 1):
+	print('x is ', x)
+	print('typeof x is ', typeof(x))
+
+var inferring := 2
+func inferred(x: float = inferring):
+	print('x is ', x)
+	print('typeof x is ', typeof(x))
+
+var weakling = 3
+func weak(x: float = weakling):
+	print('x is ', x)
+	print('typeof x is ', typeof(x))
+
+func test():
+	literal()
+	inferred()
+	weak()
+	print('ok')

modules/gdscript/tests/scripts/runtime/features/conversion_for_default_parameter.out

@@ -0,0 +1,8 @@
+GDTEST_OK
+x is 1
+typeof x is 3
+x is 2
+typeof x is 3
+x is 3
+typeof x is 3
+ok