The `with_sub_node` method is renamed to `with_optional_sub_node` to
better reflect that the non-existence of a sub node with the desired type is
ignored.
At the same time, the new `with_sub_node` now takes a second functor that is
called when no sub node of the desired type exists.
genodelabs/genode#4600
The CBE repository contained a lot of Genode-specific code despite the fact
that the CBE core logic is not bound to Genode in any way. Therefore the
Genode-specific CBE code is moved to the 'gems' repository to form part of
Genode mainline. The remaining CBE code becomes a port in Genode instead of
being invoked as sub-repository.
The commit combines the following work steps:
* add all files removed from CBE repository
* add CBE port files
* make all CBE libs and targets build again
* make all CBE run scripts succeed again
* make all CBE recipes build again
* make CBE autopilot succeed again
* let CBE autopilot use 'libsparcrypto' contrib dir and Genode build dir
instead of '.ci' dir in CBE contrib dir (remove '.ci' dir from CBE repo)
* let CBE autopilot always check for all ports
* make CBE autopilot directly executable
* fix license headers in all Genode CBE files
* remove unused VFS replay component
* remove unused CBE test
* remove unused external crypto
* remove unused files in run dir
* remove unused external trust anchor
* add cbe_tester test to autopilot list
* get rid of directories 'include/cbe_*' and 'include/utils'
Fixes#3937
