`gimp_unit_store_get_value()` clashes with the `get_value()` method of
its parent class GtkTreeStore. This means trouble for bindings, as seen
here in some pseudocode:
```vala
var unit_store = new Gimp.UnitStore();
// Which function are we referencing here, the one from GtkTreeStore or
// the one from GimpUnitStore? Worse, they both have different arguments
unit_store.get_value( ... )
```
... and G_TYPE_INSTANCE_GET_PRIVATE()
g_type_class_add_private() and G_TYPE_INSTANCE_GET_PRIVATE() were
deprecated in GLib 2.58. Instead, use
G_DEFINE_[ABSTRACT_]TYPE_WITH_PRIVATE(), and
G_ADD_PRIVATE[_DYNAMIC](), and the implictly-defined
foo_get_instance_private() functions, all of which are available in
the GLib versions we depend on.
This commit only covers types registered using one of the
G_DEFINE_FOO() macros (i.e., most types), but not types with a
custom registration function, of which we still have a few -- GLib
currently only provides a (non-deprecated) public API for adding a
private struct using the G_DEFINE_FOO() macros.
Note that this commit was 99% auto-generated (because I'm not
*that* crazy :), so if there are any style mismatches... we'll have
to live with them for now.
even if we don't have private members (yet). Also make class padding 8
pointers in all headers. This commit moves nothing to private, it just
makes all headers consistent and adjusts .c files accordigly.
_gimp_unit_store_sync_units(): don't trigger a sync of newly added
units if we encounter GIMP_UNIT_PERCENT, it has a special value that
is always larger than any other unit. All unit menus containing
"percent" were broken the same way.
Add private API _gimp_unit_store_sync_units() which emits
"row-inserted" on each unit that didn't exist when the GimpUnitStore
was created, or when sync_units() was called the last time.
In GimpUnitComboBox, call sync_units() each time the combo is popped
up, or a unit is set on the combo.
to allow having unit combos without "pixels". Adapt GimpUnitComboBox
to not assume that the unit is equal to the index in the store and
enable "menu_has_pixels" in GimpSizeEntry again.
