Move headers Part 2

[kodebach]

What happens in this PR?

Continuing from #4920, this PR includes further progress on the decisions mentioned in #4920. The goal for this PR is to finish all the header changes, i.e. src/include should (basically) have it's new contents completed with this PR.

• 38b7e17 splits the old_helper.h header into more modular units
• 5fe5bc1 is the only automated commit in this PR, it updates the files that used old_helper.h
• 807a51f and 2e97bea are the formatting fixes and manual updates necessary after the automated commit
• b455e37 until b03b163 were done manually. They split kdbprivate.h into more modular units. I did this manually, because I wanted to verify where kdbprivate.h is used and why. Partly to ensure there isn't some place that shouldn't use it and partly to inform how kdbprivate.h should be split up.
• All following commits are additional fixes required to make things actually work

Hints for reviewers

As with #4920 this PR has a large number of changed files. Most of them once again are only updated #includes.

• src/include/** split up, moved, rearranged headers according to decisions (the thing that causes all the other changes)
• src/libs/elektra/CMakeLists.txt CMake update, not sure if it's needed here, may have slipped into the wrong commit and may only required by Move headers Part 3 #4941, but doesn't break anything
• src/libs/elektra/backends.h new header extracted from kdbprivate.h
• src/libs/elektra/hooks.h new header extracted from kdbprivate.h
• src/libs/elektra/internal.c moved elektraMemcpy and elektraMemmove to keyset.c
• src/libs/elektra/keyset.c adds a new DEFAULT_KEYSET_SIZE because the old KEYSET_SIZE is no longer in a header AND moved elektraMemcpy and elektraMemmove from internal.c
• src/libs/elektra/keytest.c removal of keyIs* functions which are now static inline aliases
• src/libs/elektra/symbols.map now exports elektraReadNamespace as private (no idea how it worked before)
• src/libs/highlevel/elektra.h new header extracted from kdbprivate.h
• src/plugins/xmltool/xmltool.h removal of unnecessary redeclaration of elektraStrLen
• src/tools/kdb/gen/templates/collect.sh adds a mkdir -p (no idea what it is needed now)
• tests/ctest/test_keyset_cow.c adds a new DEFAULT_KEYSET_SIZE because the old KEYSET_SIZE is no longer in a header

All other changed files are only changes in #includes.

Those are the main changes of this PR, below are some extra fixes to please the CI:

• doc/man/** not sure why those changes were needed, but the CI complained
• scripts/docker/openwrt/sdk/Dockerfile update OpenWrt image (should happen on master at some point too)
• tests/linkchecker.whitelist add https://opensesame.libelektra.org and https://pull.libelektra.org because of certificate issues

Basics

• Short descriptions of your changes are in the release notes
  (added as entry in doc/news/_preparation_next_release.md which contains _(my name)_)
  Please always add them to the release notes.
• Details of what you changed are in commit messages
  (first line should have module: short statement syntax)
• References to issues, e.g. close #X, are in the commit messages.
• The buildservers are happy. If not, fix in this order:
  • add a line in doc/news/_preparation_next_release.md
  • reformat the code with scripts/dev/reformat-all
  • make all unit tests pass
  • fix all memleaks
  • fix the CI itself (or rebase if already fixed)
• The PR is rebased with current master.

Checklist

• I added unit tests for my code
• I fully described what my PR does in the documentation
  (not in the PR description)
• I fixed all affected documentation (see Documentation Guidelines)
• I fixed all affected decisions (see Decision Process)
• I added code comments, logging, and assertions as appropriate (see Coding Guidelines)
• I updated all meta data (e.g. README.md of plugins and METADATA.ini)
• I mentioned every code not directly written by me in reuse syntax

Review

• Documentation is introductory, concise, good to read and describes everything what the PR does
• Examples are well chosen and understandable
• Code is conforming to our Coding Guidelines
• APIs are conforming to our Design Guidelines
• Code is consistent to our Design Decisions

Labels

• Add the "work in progress" label if you do not want the PR to be reviewed yet.
• Add the "ready to merge" label if everything is done and no further pushes are planned by you.

[kodebach]

@lawli3t @atmaxinger @hannes99 @flo91 @lukashartl If you review, please read the PR description it explains what's happening in this PR and which files have interesting changes.

[kodebach]

jenkins build libelektra please

[hannes99]

LGTM and matches what was decided in the decision.

[kodebach]

jenkins build libelektra please