refactor: Use IContextMenu to dispatch right clicks

[gonfunko]

The basics

• I validated my changes

The details

Resolves

Fixes #8842

Proposed Changes

This PR updates Gesture to check for conformance to IContextMenu when dispatching right clicks, rather than hard coding specific kinds of elements.

Although Gesture is still fairly closely tied to specific elements, in general this does open a path for things to just implement IContextMenu to get context menu support. Clicks bubble up from e.g. fields to blocks to the workspace, with each item informing Gesture of a click in turn, and the workspace handler is what ultimately triggers the right click handler. Thus, as long as an element (a) gains focus on (right)click, (b) is a child of the workspace, and (c) implements IContextMenu, Gesture should now trigger display of the context menu when it is right clicked.

While I was here, I also cleaned up the bringing-block-to-front behavior. This was being triggered in various block sub-elements (fields, icons), but because of the bubbling behavior described above, clicks on those will ultimately reach the parent block, so performing bring-to-front when the block becomes the target block covers all these cases, for both left and right clicks.

[BenHenning]

Thanks @gonfunko! Just one comment to double check one of the bringBlockToFront removals that I don't think is covered by tests, but otherwise this LGTM.

[BenHenning]

Just to check, did you validate this bit is no longer needed? I.e. that using keyboard nav to end field editing correctly returns focus to the block? (I think that was the case that necessitated this originally).

[gonfunko]

AFAICT behavior is unchanged; if you focus a field via keyboard, hit enter, change it, and hit enter, the field gets focus when editing is committed. If you click on a field, make changes, and hit enter, the parent block gets focus, which is consistent with the behavior I see on the hosted keyboard experiment demo page.