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
This saves on a 1500-line import at startup and may be skipped entirely
if no compiled languages are used. In exchange, we move the
implementation to a new file that is imported instead.
Followup to commit ab20eb5bbc.
Linkers that aren't actually ar, were refactored into a base class in
commit 253ff71e6b, which however didn't
take into account that we were doing checks for this.