Focus lost when adding an item to a string array setting

[RMacfarlane]

Issue Type: Bug

1. Open settings editor and search for a setting of type string[], like keyboard.touchbar.ignored
2. Start adding an item, type something, tab to the ok button and press enter

I no longer see a focus indicator anywhere, and if I want to continue using the keyboard to edit the setting, I have to tab back through to "Add item". I think it would be a better experience if focus returned to the setting that was just edited.

VS Code version: Code - Insiders 1.38.0-insider (8cd00a7, 2019-08-27T06:10:29.182Z)
OS version: Darwin x64 18.7.0