[TimePicker] Digital: always open keyboard, select all, OK on Enter

[ltguillaume]

Is your feature request related to a problem? Please describe.
The digital time picker is far from intuitive in its current state. I propose three simple usability improvements.

Describe the solution you'd like

1. Always open the on-screen keyboard upon being triggered
   The keyboard is alway necessary to make use of the picker, so it doesn't make sense to have it closed at first.
2. When clicking either field, always select all its contents
   This way, the user can start entering a value right away. Additionally, it would solve the strange behavior of ignoring user input and switching to the minutes input (placing the cursor at the end of the value) when entering a number while the cursor is at the end of the hours input (and hours value >9 is already present). This really complicates reliable input.
3. Enter button should act as OK
   When in the minutes field, the keyboard's Enter key should confirm the input (i.e. act as the OK button), instead of just closing the keyboard.