Use project-files to know which directory watchers to skip

Use project-files to know which directory watchers to skip

The directory-finding logic is probably a bit slower than using
eglot--directories-recursively, but since it honours `.gitignores` and
ignores more directories it's much faster overall.  And guaranteed to
create less watchers.

Thanks to Dmitry Gutov <dgutov@yandex.ru> for the idea.

* eglot.el (eglot--directories-recursively): Remove.

GitHub-reference: per https://github.com/joaotavora/eglot/issues/697