More intuitive navigation between groups

[kaycodes13]

Summary of Changes

This PR closes #75 by:

• Giving INavigables the option of providing a choice of multiple selectables for each incoming navigation direction.
• Changing SelectableWrapper to pick from these options based on distance and how shallow the angle is between selectables in the given axis of travel.
• Changing VerticalGroup to offer a choice of any of its selectables when being navigated to from the left or right
• Changing GridGroup to offer a choice of its leftmost/topmost/etc selectables from each row/column when being navigated to from each direction.

The "Scrolling Pane Tests" menu has multiple Grid and Vertical groups laid out beside each other and nested in various ways so it makes a decent testing ground for the new behaviour.

Some methods in INavigable and INavigableExtensions have had their names and parameter types changed so this does have some breaking changes; it might affect mods that set up navigation between elements manually with a FreeGroup.

Checklist

• No change is too small for a release, so pick one:
  • I have updated the package version following semantic versioning
  • There is another change actively WIP that will update the version
  • This PR does not update user-facing code/config
  • I'm not sure how to set the version and would like the reviewer's help

[kaycodes13]

(version bump added as per flibber's suggestion on the other PR)