This patch supports the Cryptomatte picker in the 3D viewport. Instead
of picking a color from the viewport GPU texture, we instead sample the
scene directly to get the object or material under the cursor, then hash
their names to get the Cryptomatte hash value. We do this because the
viewport texture have limited precision, so it can't store the
Cryptomatte hash values.
Additionally, we adjust the Cryptomatte session code to extract the
Cryptomatte manifest from the scene directly, as opposed to the
RenderResult. This is done to make it work even when no RenderResult
exist, as is the case for the viewport compositor, which is needed
especially after #123378.
Pull Request: https://projects.blender.org/blender/blender/pulls/123815
4cd1245396