Add a skipFilledCells prop

[jc4p]

Adds an optional prop to implement "skip to next open tile" functionality similar to NYT Mini.

If the second row across is filled and you're on the first row going down, when you enter a letter it skips past the second row into the third.

[cbeav]

Thanks so much for the pull request! Three things:

1. If we want this as a prop on the project, we'd probably want to expose it on CrosswordSolver and not CrosswordGrid, as that's the higher-level component that most clients (including MiniWord) would use
2. I actually like this better as the default behavior; I've been meaning to implement it for a while. I think if we get the behavior down right we can ship it enabled by default and you'll be happier in MiniWord once I update that
3. Noticed a bug here. When you change the active cell (by clicking/tapping for example) to not be the first empty cell in the answer, any input will be confusingly jumped to the first empty cell. Even more confusing if the answer is complete: the user sees no changes at all (at the end of attached video I'm typing and nothing is happening in the word). You had to delete (via backspace) something in the word in order to be able to type in it and advance to next letter/word

Screen.Recording.2025-05-09.at.12.48.26.PM.mov

[jc4p]

Pushed change moving it to CrosswordSolver -- got a repro of the bug, trying to nail them :)