It's just too weird to be public. Remove its properties from the wire
protocol and from pluginrc. Instead, have all GParamSpecs' flags on
the wire and in pluginrc, so we can use stuff like
GIMP_PARAM_NO_VALIDATE.
Port the remaining few places to GIMP_PROC_ARG_STRING().
I'm sure something is broken now wrt UTF-8 validation,
will add tighter checks in the next commit.
This partly reverts commit d999248d70.
The GimpStringArray is still very weirdly handled, in particular
regarding the difference of processing with static_data set or not.
Still this g_return_val_if_fail() was making more problems. It may come
back but will need more coding to handle the side effects.
Our GimpStringArray is so weird. We are obviously expecting it to be
NULL-terminated since, when we duplicate the data, we add one value.
Yet we were not checking that the stored data was NULL-terminated, in
particular when the string array is created with static data (in which
case, we use the input data as-is, without re-allocating).
Note that this doesn't fix the type mismatch Gimp.StringArray vs
Gimp.Array when introspecting.
all the stuff from app/core/gimpparamspecs.[ch] that is not about
image, drawable etc IDs, these will have to go to libgimp with
different implementations than in app/.