Add when context: isLastGroup / isFirstGroup / editorGroupIndex / isLeftGroup / isRightGroup / isTopGroup / isBottomGroup

[jaydenwindle]

This PR addresses #22755 by adding several context keys to support the configuration of keyboard shortcuts based on which editor group is currently active.

[msftclas]

All CLA requirements met.

[jaydenwindle]

It is worth noting that in the current implementation, the isFirstGroup and isLastGroup context key values do not always correspond to the leftmost and rightmost editor groups visually, but instead to the order in which the groups were opened. For example, when stacking groups vertically or rearranging them horizontally:

To be maximally useful to the original use case, it would be best to have the isLastGroup and isFirstGroup context keys set when the leftmost or rightmost editor group is active, or to create separate context keys (e.g. isLeftGroup and isRightGroup) to denote that.

[jaydenwindle]

Update: I've added an (albeit hacky) implementation for isLeftGroup and isRightGroup context keys, as well as for isBottomGroup and isTopGroup.

Currently it works for the editor group configurations I've tested (see demo attached), but type casting to get access to the IEditorGroupView and then doing raw element getBoundingClientRect calculations seems much less than ideal. I'd love some tips on how to do this in a cleaner way.

Also, I haven't found a good way to write unit tests for these changes since there are some fairly complex editor setups that need to be tested. Any advice on how to proceed there would be amazing.

Demo: https://cl.ly/f0cdf8af9bc7

[bpasero]

Thanks for the work but I ended up implementing this a bit different given some new support that I added recently. See 406b1f3