Refactor deep ternary operator

[knokmki612]

the following code feels difficult to read or maintain. for example, it will be better to externalize as function.

jolla-kbd-flick-jp/src/layouts/ja_10key_flick/AssistLabel.qml

Lines 15 to 24 in 670ea40

	horizontalCenterOffset: keyIndex == 2 || keyIndex == 4
	? 0
	: (keyIndex == 1
	? -offset
	: offset)
	verticalCenterOffset: keyIndex == 1 || keyIndex == 3
	? 0
	: (keyIndex == 2
	? -offset
	: offset)