[$] The first half of the 6.6 merge window

As of this writing, 4,588 non-merge changesets have been pulled into the
mainline repository for the 6.6 kernel release. The 6.6 merge window, in
other words, is just getting started. Nonetheless, a fair amount of
significant work has already been pulled, so the time has come to summarize
what has happened so far in this development cycle.