Merge branch 'blackbeard/T10930-load-avb' of https://invent.kde.org/albertofl/krita into blackbeard/T10930-load-avb

OpenGL 2.1 systems are supported, but Small Colro Selector is not
available for them, because it doesn't have legacy shaders (needs
to be implemented).

CCBUG:408872

Before this commit if you first selected the color model,
then color profile, then color depth, the color profile would switch to
default for this color depth no matter that the user just set it
manually. This is mostly the problem if someone is for example using
Rec2020 profile for HDR images and switches between 32 and 16 bit
color depths.

Behaviour now:
- by default color profile changes to the default one that suits
the color model and color depth
- if the user sets the profile manually, it is remembered
and if it changes color depth, the profile doesn't change
(keep in mind that "(Default)" suffix is still attached
to the default profile, so it's easy to find in case the user wants it
- if the user changes the color model, the default behaviour
(switching profile automatically) is restored until the user
sets up the profile maually again.

BUG:406700

They cause artifacts and we don't have a fix yet :(

CCBUG:404133

Note from the committer:
This commit was initially made on krita/4.2 branch.
However between 4.2.1 and 4.2.2 the stable branch was
reconstructed, which caused all commits that were exclusively
on the previous krita/4.2 (and not on master) to be missing.

The previous commit hash: d3e4c3aa

Also regarding the artifacts: it never worked, optimization were
enabled during the creamy flow implementation, but they never should
be enabled until someone fix them properly.

ShapeGroupContainerModel::remove() will call KoShapeGroup::invalidateSizeCache(),
even when the shape group is going to be destroyed. This method is called after
KoShapeGroup's destructor, so at this time we no longer have access to members of
KoShapeGroup, i.e. its d-pointer. So this call will cause access violation as the
instance `QScopedPointer<Private> d` in KoShapeGroup has already been destroyed.

This is a result of getting rid of derived d-pointers, because if we use a derived
d-pointer, it only gets destroyed in the ancestor class (KoShape). We temporarily
fix this problem by manually call `model()->deleteOwnedShapes()` in KoShapeGroup's
destructor.

CCMAIL:tusooa@vista.aero

This fixes a crash when pressing cancel when you're trying to
create a RGB8 linear gamma image, which shouldn't be possible.

The class KisSharedDescendent used to be employed to wrap up
derived d-pointers, but since we have already refactored them
out, there is no reason to keep them now.

KoImageData was explicitly shared, and the implicit sharing
breaks TestImageCollection

These two class templates are used to store any subclass of a base class.
KisSharedDescendent is also inherited from QSharedData, and its use for
copy-on-write is documented in the comments.