feat: initial feature-flagged, draft new autocompleter MONGOSH-2036

[lerouxb]

Still a draft, don't merge :)

Most of everything is stubbed or TODO and this needs tests. But hopefully it is reasonably close to the interface we're going for.

NOTE: It requires mongodb-js/devtools-shared#520, but that in turn depends on a different mongosh PR so this is broken right now.

~/mongo/devtools-shared/packages/mongodb-ts-autocomplete % npm link

then

~/mongo/mongosh % npm link @mongodb-js/mongodb-ts-autocomplete -w @mongosh/cli-repl

then

~/mongo/mongosh % USE_NEW_AUTOCOMPLETE=true npm run start -- 'your connection string here'