[21767] Added support for splash images for iPhone XR and XSMAX

[livecodepanos]

1. Added new groups for iPhone XR and XSMAX
2. Modified existing UI to fit all necessary fields.

Binary changes:

In group "Splash Screens":

the ... buttons for splash screen selection have the following code, for iPhone XR and XSMAX, for portrait and landscape respectively:

on mouseUp
   chooseImageFileWithDimension "iPhone XR Portrait splash", "828,1792"
end mouseUp

on mouseUp
   chooseImageFileWithDimension "iPhone XR Landscape splash", "1792,828"
end mouseUp

on mouseUp
   chooseImageFileWithDimension "iPhone XSMAX Portrait splash", "1242,2688"
end mouseUp

on mouseUp
   chooseImageFileWithDimension "iPhone XSMAX Landscape splash", "2688,1242"
end mouseUp

Also changed the tooltips that specify the required dimensions accordingly.

The X buttons for clearing the selected splash screens for iPhone XR and XSMAX (for portrait and landscape respectively) have this code:

on mouseUp
   clearSetting "iPhone XR portrait splash"
end mouseUp

on mouseUp
   clearSetting "iPhone XR landscape splash"
end mouseUp

on mouseUp
   clearSetting "iPhone XSMAX portrait splash"
end mouseUp

on mouseUp
   clearSetting "iPhone XSMAX landscape splash"
end mouseUp

[montegoulding]

@livecode-vulcan review ok 70828b6

[livecode-vulcan]

💙 review by @montegoulding ok 70828b6