This formats all copyright comments according to SPDX formatting guidelines.
Additionally, this resolves the remaining GPLv2 only licensed files by relicensing them to GPLv2.0-or-later.
Add a std::bit_cast-like function archiving the same runtime results as
the standard function, without compile time support.
This allows us to use bit_cast while we wait for compiler support, it
can be trivially replaced in the future.
