[AutoComplete] Use new context api

[AndrewMusgrave]

WHY are these changes introduced?

Part of #1377

WHAT is this pull request doing?

Nothing special, using the new context API and updating tests

[alex-page]

Looking at the examples in storybook it all looks gravy. I still recommend resolving the conversations with Ben before merging.

[BPScott]

I still recommend resolving the conversations with Ben before merging.

I'm happy to say merge this as is (+ fixing that autoimport goof) as it follows the current style, then we can go back and update all context usage to be a context.ts instead of a subcomponent in a follow-up PR once the existing legacy context migration PRs are merged (per Andrew's comment).

I think it's worth doing the tidy-up PR once the existing context migration PRs are merged, rather than waiting till all legacy context usage has been migrated, as migrating straight to the final new pattern of context living in a context.ts sounds like less work than migrating a component to use a context subcomponent, and then migrating to the context sub component to a context.ts.

[BPScott]

Fixup the accidental absolute path, then this is good to go

[danrosenthal]

Code changes look great!

I'm a bit surprised no tests needed to be changed with this. Either we did a great job of writing those tests initially, or coverage was never there.