Add helpful entry widgets that set up validation and appropriate keyboard types

[Jacalz]

Moving this on from fyne-io/fyne#916. We should be supporting the restriction of input types in things such as entry on mobile where you might want to only allow number inputs for examples.

[andydotxyz]

Just to re-add some of the context from where this ticket came from we wonder if this is possible to deduce based on the validator in use rather than through manually setting by the developer

[AlbinoGeek]

Honestly though, overriding mobile.Keyboardable or w/e wasn't too bad (for Spinner) -- I didn't mind that.

[andydotxyz]

Hmm, not sure what more we should do here.
Extend validator to provide keyboardable (optionally) or add pre-configured entries (perhaps to fyne-x)?
Thoughts @Jacalz ?

[Jacalz]

Hmm, I think it would be strange to wrangle the validators in a way to restrict the keyboard input. I'd go with https://developer.fyne.io/tutorial/numerical-entry and then possibly have entries in fyne-x whith has that restriction set.

[andydotxyz]

Agreed, so I guess this ticket is completed then?

[Jacalz]

More or less, yeah. Might be a good idea to close when we have the extended widgets in fyne-x? Or open an issue there maybe?

[andydotxyz]

Transferred the whole ticket to fyne-x repository :)