Splits and equalizing on splitting

[jonathanj]

In #831 the equalize-splits command was added, I'd like to suggest going one step further: Have an option to automatically equalize splits after splitting. iTerm 2 splits behave this way by default.

There are some quirks to equalizing though, for example if I do: split right, split right, split bottom, split right:

If I equalize splits now, I would expect that my right splits each become 1/3 wide, and my bottom split becomes 1/2 high, however that's not quite what happens:

The right splits are not divided equally into thirds, and the bottom split is not divided equally into halves. I'm not sure I can understand what happened, but it wasn't what I was expecting.

For reference, this is what my sequence of splits produces in iTerm 2:

[jonathanj]

FYI, if I change my sequence in ghostty, it will produce the same thing as iTerm 2: split right, split right, equalize splits, split bottom, split, right

[JakeWharton]

Answered in #3839, resulted in #2227 (comment)