The user doesn't need to delete the current input before changing it. He can now write
hiw new value which will erase the current one.
The guest popup from the `pos_restaurant` module and the global discount popup from the
`pos_discount` module benefit from this and have their input pre-selected.
Before: when opening the guest or discount popup, the user always has to delete the curent
value before changing it. Let's say that the current value was `5`, the user needs to either
press the `Delete` or `Backspace` button/key before entering his new value.
After: the user doesn't need to press the `Delete` or `Backspace` button/key and can now directly
enter his new value
Task ID: 2419637
Jacky (trj)
13843f8545