Add support for completion behind user's cursor

[AndiLavera]

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Example of Cursor (the Vscode fork) prediction suggesting changes before and after the cursor point:

In Cursor, when a completion is forward only, it looks like the normal ghost text. When the suggestion includes a completion behind the users cursor, the editor displays the suggestion to the right side as a small window.

[ericdallo]

@AndiLavera can you elaborate this one with more examples/code? I think it makes sense to match cursor, but I'm not sure I got what was completed from that image / what we should support exactly

[AndiLavera]

Please ignore the contents of the code. I was clicking around, letting Cursor tab complete drive itself.

Suggestions that I would say are "behind the users cursor":

> My cursor was after the string on line 5. Not sure why the icon isn't in the photo.

Other potentially interesting views:

For these two, it looks like if the suggestion has any removals, Cursor displays the floating window instead of ghost text.