Inserter: Include block description when searching for blocks

[ryelle]

The Block Directory search includes the description, so it's possible to have a block that is found via the directory but not locally. I think this is the issue behind #24911 — in that case, the installed block doesn't use the phrase "maps" in any of the currently-searched fields, so it won't show up.

You can also reproduce this with just core by searching for "snippets", a word that shows up in the code block description - but no blocks will be found here.