compositor: introduce wlr_surface_set_role_object()

This allows to set the role without setting a role object.

Tested:

• Trying to assign a different role fails and ­sends an error
• Trying to assign a role for a surface with an existing role object fails and sends an error
• Causing a role object initialization error after setting the role fails correctly and doesn't call the destroy hook on uninitialized memory

Breaking changes

• wlr_surface_set_role() doesn't take role_data now, which must be set separately with the new wlr_surface_set_role_object() function instead. A role object can only be set once and can't be changed until wlr_surface_destroy_role_object() is called. If a role is represented by an object but the surface has no role object set, the role commit and unmap hooks aren't called.

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Supersedes !4207 (closed)