Add `hasMulipleLayouts`

[phistuck]

A keyboard legend that is shown according to the current layout can be confusing, because the layout changes when the user presses Alt + Shift (on Windows). What do you expect the legend to do when the layout changes while the legend is shown? Change the keys immediately and show the new keys? What if the user comes with a certain layout (because that was the last layout they used, not because this is the layout that are used to)?

If the legend knows the user has multiple layouts (it does not matter what the layouts are), it can at least communicate that to the user ("This legend is shown according to the current typing language, change typing language to see the matching keys."). Otherwise, it can be confusing (A on German layout is Q, but both of them exist in both of the layouts, so which one did the legend referred to?)