This finds the core resource knowing its type, name, collection and internal
state (in other words, the values returned by _gimp_resource_get_identifiers()).
Rather than reimplementing the same checks for every possible resource data
type, just do it once and redirect to the correct factory container.
For the libgimp API, we leave per-type functions `gimp_*_get_by_name()` (where *
can be brush|gradient|font|palette|pattern so far), but internally they all use
gimp_pdb_get_resource().
Note that eventually we want these functions to return a list of resources as it
should be possible to have several resources of a given type with the same name
(since they are made by third-party who might have had the same idea of a name).
Much like for images and items. Change the PDB to transmit IDs
instead of names for brush, pattern etc. and refactor a whole
lot of libgimp code to deal with it.
modified: libgimp/gimpplugin-private.h
Jehan