This replaces all of the Apache blurbs at the start of each file with an
`# SPDX-License-Identifier: Apache-2.0` string. It also fixes existing
uses to be consistent in capitalization, and to be placed above any
copyright notices.
This removes nearly 3000 lines of boilerplate from the project (only
python files), which no developer cares to look at.
SPDX is in common use, particularly in the Linux kernel, and is the
recommended format for Meson's own `project(license: )` field
Split out checking of file format as a separate GitHub workflow, rather
than running it as part of the project tests for every platform and
toolchain combination in CI, so that this test is not effected by the
changed paths constraints which are applied to the project tests.
Charles Brunet