Scaffold: Allow panel to specify supported dock locations

[ldosmorbrian]

Update how we configure the buttons in some appropriate way to allow for naming which buttons are available.
Keep dockLocationButton: true as you have it – and if the config specifies that without the below customizations – then it will work just as you have it – showing all supported dock locations on the menu.

But allow customization such that the developer can specify an array of supported locations. * This will allow us to specify something like [ "left", "right" ] — implying the panel can only be docked to the left or right, but does not support being docked to bottom or modeless.

This matters because certain events are treated differently in for example "modeless".
Some panels may have custom designs that don't make sense to open at "bottom" so it will be better not to provide unsupported options to the user.

Config Example1: only specifies dockLocationButton: true * Will show all dock buttons

Config Example2: only specifies dockLocations: [ .... ] * if the array is empty no buttons are displayed

any supported location string in the array will show the button — the order of the buttons on the panel should NOT be different than the usual order, regardless of how they are ordered in the array.
if an unsupported location is in the array, then it is ignored.

Config Example3: specified both dockLocationButton AND dockLocations array * when dockLocationButton is false the dock location button will not be displayed for the panel, regardless of the other dockLocations array.

when dockLocationButton is true when there is also a dockLocations array, then the treatment of the dockeLocations array is the same as Config Example2 above.

Reference: 11867