feat: add VIAL support for xt60_singa

[Blood13]

So, the firmware for the xt60_singa is ready.

• Support for both VIA and VIAL (except for the Key Override function due to the image size limitations).
• Fixed a bug with the inverted CapsLock, relevant for white hot-swap boards. When CapsLock was pressed (LED lit up), lowercase letters were typed, and vice versa: when it was off, uppercase letters were typed. Essentially, the CapsLock LED was always on in its normal state, which was extremely annoying.

[lesshonor]

If this was an ARM board these would just be nitpicks, but atmega32u4 (especially with RGB enabled) needs all the help it can get to keep filesize down.

[lesshonor]

No need to hardcode filler KC_TRNS layers. Dynamic keymaps will automatically fill in "missing" layers at compile-time up to the maximum set in dynamic_keymap.layer_count. (By default, this is 4.)

Suggested change

	),
	// Fn2 Layer
	[2] = LAYOUT_all(
	KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS,
	KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS,
	KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS,
	KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS,
	KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS
	),
	};
	)
	};

[lesshonor]

Suggested change

	"name": "XT60_SINGAKBD",
	"vendorId": "0x4B50",
	"productId": "0x0601",

These attributes are not used by Vial.