Start the merging-rebase to v2.30.1

This commit starts the rebase of 52de3c5 to 36b80a5

We are using this opportunity to reorder some patch series into the
`ready-for-upstream` section, and we also rebase the `git maintenance`
patches that so frequently caused merge conflicts during the update of
the ever-green branches (i.e. the branches that are continuously rebased
on top of upstream's integration branches).

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho