Minesweeper: add mouse "chording" feature

[RetiredWizard]

@makermelissa This adds the mouse "chording" (both keys pressed) feature we discussed briefly on an earlier PR.

I believe in the Microsoft version the highlighted tiles used the OPEN [ 0] sprite but I'm using the MINE_QUESTION_OPEN [15] sprite because it's not being used anywhere else and therefore I don't need to set up a separate tracking array for the highlighted cells. I could update the sprite sheet to replace the question mark with a blank open cell but I think the question mark works fine.

[RetiredWizard]

This update does require adafruit/Adafruit_CircuitPython_USB_Host_Mouse#11 which was just merged so if you're testing before the new library is published you may need to grab the source from github.

[RetiredWizard]

I added dx, dy to _get_board because pylint didn't like the number of if statements in my new methods. Calling _get_board without the dx,dy parameters results in the method behaving exactly as it did before so there should be no further changes required.

That being said, I could also update all the existing calls to _get_board to use the new parameters reducing the number of if statements in other methods. This would result in the _get_board function being called more often which probably is not quite as speed efficient. If you like this idea, I could also update _set_board in the same way although the only place it would impact is the new square_chord_highlight method.

I could also restore the _get_board function as you originally had it and just disable the pylint too many branches check.

[RetiredWizard]

Out of curiosity I asked chatgpt to help with resolving the pylint too many branches issue and it came up with this approach which I liked.

While testing I also noticed that clicking outside the game board and then moving the mouse to the board without releasing the mouse button was causing a crash so I added some tests to check for out of board clicks.

[makermelissa]

Looks good. Tested and works great.