Instead of lengthy blurbs, switch to single-line, machine-readable
standardized (https://spdx.dev) license identifiers. The Linux kernel
switched long ago, so there is strong precedent.
Three cases are handled: AGPL-only, Apache-only, and dual licensed.
For the latter case, I chose (AGPL-3.0-or-later and Apache-2.0),
reasoning that our changes are extensive enough to apply our license.
The changes we applied mechanically with a script, except to
licenses/README.md.
Closes#9937
Asias He reports that git on Windows filesystem is unhappy about the
colon character (":") present in dist-check files:
$ git reset --hard origin/master
error: invalid path 'tools/testing/dist-check/docker.io/centos:7.sh'
fatal: Could not reset index file to revision 'origin/master'.
Rename the script to use a dash instead.
Closes#7648
