Focus all windows only on mouse clicks

[Riteo]

Fixes #40227.

Apparently all windows would get instantly focused on any input event, making it impossible to move from the OptionButton to its popup without refocusing its parent window and closing it.

I have no idea if that was intended behaviour, if it is, feel free to close this PR.

[bruvzg]

I can't reproduce the issues, and do not see any difference in behavior.

[Riteo]

@bruvzg sorry, I should have specified it here too: this fixes an issue that happens only on single window mode.

[bruvzg]

I should have specified it here too: this fixes an issue that happens only on single window mode.

Reproducible in single window mode, but only with some option buttons. And fixed by this PR. But it's not entirely clear why it's happening and why it's affecting only some buttons.

Also, need to be tested to not break input on non embedded windows (it seems to work fine on macOS and Windows).

[Riteo]

But it's not entirely clear why it's happening

According to my tests with gdb every single time I've reproduced this issue (although with only two OptionButtons, one of which is reportedly working, but not for me) the backtrace always pointed to a window focusing function. I can't give my usual very big and detailed messages because I'm not at my computer right now, but just know that according to my tests I'm pretty sure this is the cause.

[Riteo]

Apparently this whole approach isn't the right solution, so I'm closing this PR.