Creates a new keyboard with the same buttons but reflowed into a given number of columns as if the buttons were text elements. Optionally, you can specify if the flow should make sure to fill up the last row.

This method is idempotent, so calling it a second time will effectively clone this keyboard without reordering the buttons.

Here are some examples.

original    flowed
[  a  ]  ~> [  a  ]    (4 columns)

            [  a  ]
[a b c]  ~> [  b  ]    (1 column)
            [  c  ]

[ a b ]     [a b c]
[ c d ]  ~> [ d e ]    (3 columns)
[  e  ]

[ a b ]     [abcde]
[  c  ]  ~> [  f  ]    (5 columns)
[d e f]

[a b c]     [  a  ]
[d e f]  ~> [b c d]    (3 colums, { fillLastRow: true })
[g h i]     [e f g]
[  j  ]     [h i j]