Improve Slash command search prioritiziation

[jasmussen]

We should consider improving how the slash command filters results. Right now, if you search for /image and press Enter, you get a Cover Image block. Presumably you wanted the Image block. This happens because C sorts before I alphabetically, but in practice this feels like the wrong behavior for the search command.

GIF:

Although I only occasionally use the Cover Image block, I've mistakenly inserted it using the Slash command so often, it now shows up under Recent Blocks.

[karmatosed]

This seems like a great enhancement.

[bph]

more examples for surprising suggestions for slash command search see gif.

1. /t included heading and paragraph block
2. /q only shows Quote (not Pullquote)
   

[jasmussen]

Noting that the original intent of this issue is fixed in master now, and typing /ima gets you an Image, not a Cover Image. Keeping open per #5158 (comment)

[mtias]

Closing in favor of #5643 for further improvements.