Make global summon focus the search box

[joadoumie]

Related to #306 as clicking right now takes focus away from the search box.

We need to ensure that the keyboard shortcuts are always captured and that the search box pretty much always has focus (as it is responsible for the keyboard handling + it also is just really important to always be able to filter).

This also relates to #271 because in that flow, it actually does take focus away from the search box when you relaunch the palette.

[zadjii-msft]

Fixed in #326