✨Add support for ilia desktop executor

Ilia is used by Regolith Linux (Ubuntu+i3/sway).

Ilia has a slightly different presentation and prompt setup than other
pickers, and it makes more sense to use the given GTK icon instead of
the emoji character since that is what it seems to support.

Nicely explained by @jc00ke here:
https://github.com/marty-oehme/bemoji/pull/21#discussion_r1306212419

With the growing amount of picker tools supported out of the box
it seems more practical to have them together in a simple list
that can grow and through which we can always iterate instead
of a cumbersome growing if-else chain.
This commit also refactors the pick tool selection to be stored in
a bash hash map instead.

CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+- Add default support for `ilia` gtk-based picker tool, used by default in Regolith Linux
 - Pass through return code 1 from selection tool
 - (!) Number of displayed recent emoji can be set with `-P` option:
   This replaces previous `-P` history flag toggle. Use number to set amount of recent