Double tab autocompletion shortcut

HI,

this is an idea for enhancement:

why not using the fact that you can press more times tab , after the autocompletion window appears?

For instance in Rstudio, by pressing a 2nd time you insert the 1st suggestion of the list (this is very handy).
Another possibility would be to use tab to cycle through the suggestions.

No file or test is named. Start by locating the notebook autocomplete popup and its keyboard handling, then determine whether a second Tab should accept the first suggestion or cycle through suggestions. Done should include an agreed interaction and tests covering repeated Tab presses.

Written by the indexing model from the issue text.