Query input: select completion item on Enter keypress

Created by: olafurpg

Previously, pressing enter in the query editor would always trigger a search including when the editor displayed completion suggestions. Now, the query editor selects the completion suggestion instead.

With this change, it's possible to type lang:T, press enter to select the lang:TypeScript completion and enter again to complete the search. Previously, a Tab press was required to select the completion item. The new behavior is more consistent with the defaults in VS Code and IntelliJ.

Short recording explaining the change more in detail: https://www.loom.com/share/51a44a532fcb4085858d5741188bab67