bug#50733: 28.0.1; project-find-regexp can block Emacs for a long time

[Gregory Heytings]

> Btw, I don't understand why we focus on general-purpose text-searching 
> tools for these features.  Why not focus on packages like ID Utils 
> instead, they are so much faster.  Daniel, could you time the same 
> search in that large tree when xref-search-program is 'gid'?  (You'd 
> need to run 'mkid' first, to create the ID database, but that is 
> one-time, and is very fast.)  As I told many times, I think this is the 
> future: program language sensitive tools that use a precomputed DB.

id-tools are useful, but they do not provide the same functionality as 
grep/ripgrep.  On Emacs' trunk, mkid takes a few seconds to create a 12 MB 
database, and gid Eli returns only 4 occurrences.

This can be improved by using mkid --default-lang=text, but then mkid 
takes no less than 30 minutes (!) to create a 205 MB database, and gid Eli 
now returns 25 occurrences in ~1 second.

In comparison, rg Eli returns 6474 occurrences in < 0.1 seconds.

Moreover, incremental updates are not implemented in mkid.