GDScript: Fix MIN_INT not representable as numeric literal

modules/gdscript/tests/scripts/parser/features/number_literals_with_sign.gd

@@ -0,0 +1,17 @@
+func test():
+	print(-9223372036854775808 == (1 << 63))
+	print(-2)
+	print(- 2)
+	print(---2)
+	print(3 - 2)
+	print(3-2)
+	print(3---2)
+	print(-3 - 2)
+	print(-3 - -2)
+	print(-(3 - 2)-2)
+	print([1, 2, 3][0]-1)
+	var t = 1
+	print(t-1)
+	print(-0xFF)
+	print(1--0xFF)
+	print(floor(PI-1))

modules/gdscript/tests/scripts/parser/features/number_literals_with_sign.out

@@ -0,0 +1,16 @@
+GDTEST_OK
+true
+-2
+-2
+-2
+1
+1
+1
+-5
+-1
+-3
+0
+0
+-255
+256
+2