Pwsh autocomplete

[Tyriar]

Part of ##154662

It's a bit rough around the edges currently but it's behind the terminal.integrated.shellIntegration.suggestEnabled setting

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After chatting with @jrieken and further thinking, this is the approach I'm taking for the workbench suggest widget:

workbench/services/suggest will extend the editor/suggest where trivial, otherwise things will be forked. This will make the review/abstraction/etc. burden on editor/suggest low.

If it makes sense to avoid editor components in certain parts of editor/suggest later, we could move some to platform. That's not that important from my perspective though.

[Tyriar]

@meganrogge this is ready for a review, I'd like to get it in asap so I can start doing smaller incremental changes and track things in issues. Everything is behind a new setting so it should be fairly safe. It's not worth doing a big review of the suggest stuff as it's mostly a fork with parts commented out, which will get cleaned up later.

[meganrogge]

👏🏼