General p4est and libsc update

[cburstedde]

Describe your changes here:

Bump p4est and libsc to latest version. This entails the following:

• Update submodules
• Port latest changes of the autotools build from p4est, libsc to t8code
• Move doxygen configuration and output under doc, same as with p4est and libsc
• Prevent p4est from overrunning P4EST_OLD_QMAXLEVEL
• Couple small optimizations to hex and quad code.

I may still be missing some ports but it's all working for me.

All these boxes must be checked by the reviewers before merging the pull request:

As a reviewer please read through all the code lines and make sure that the code is fully understood, bug free, well-documented and well-structured.

• The author added a BSD statement to doc/ (or already has one)

• The code compiles without warning in debugging and release mode, with and without MPI (this should be executed automatically in a github action)

  If the Pull request introduces code that is not covered by the github action (for example coupling with a new library):

  • Should this use case be added to the github action?
  • If not, does the specific use case compile and all tests pass (check manually)

• All tests pass (in various configurations, this should be executed automatically in a github action)

• New source/header files are properly added to the Makefiles

• New Datatypes are added to t8indent_custom_datatypes.txt

• The reviewer executed the new code features at least once and checked the results manually

• The code is covered in an existing or new test case

• New tests use the Google Test framework

• The code follows the t8code coding guidelines

• The code is well documented

• All function declarations, structs/classes and their members have a proper doxygen documentation

• All new algorithms and data structures are sufficiently optimal in terms of memory and runtime (If this should be merged, but there is still potential for optimization, create a new issue)

• If a new directory with source-files is added, it must be covered by the script/find_all_source_files.scp to check the indentation of these files.

• If this PR introduces a new feature, it must be covered in an example/tutorial and a Wiki article.

[cburstedde]

The --with-p4est and --with-sc flags still create a build that depends on libsc.la/libp4est.la. This is the same behavior as previously, in that sense the PR does not make things worse. How would you like merging this one if no other issues prevail, and removing the intalled .la dependency in a separate PR?

[holke]

Thanks for the update.
This is looking all good.
Since it changes the build system and submodule, i want to wait for a full test-suite (without the less-tests option) to pass before merging: https://github.com/DLR-AMR/t8code/actions/runs/4597945781