Schedule entries tabindex on mouse-only inputs

[Joelius300]

When creating (or editing) an activity and filling in the information with the keyboard, I like to use tab and Shift+tab to switch between the input fields. This already works well but in the schedule entries dialog, the controls for the date picker and time picker are also focused when using tab. Since those can only be used with the mouse, I personally think they should be ignored when tabbing through. Also, while I can open them with space or enter, they are not keyboard-closable afterwards and force me to switch to the mouse.

Current (production 05.07.24):

I think it would be nice to ignore these four:

If you agree with this change, I think it could be easily implemented with tabindex="-1" but I have not looked into the code at all. Ps. I also think #5129 would be a big QOL improvement, especially 1000 = 10:00 for numpad users.