Android interprets char as unsigned char, so comparing with 0 triggers a
tautological-unsigned-char-zero-compare warning.

Casting c to an unsigned char and removing the comparison with 0
resolves the warning while needing one less comparison on all platforms.

Now superseded by Common::FromChars

Obsoletes these functions in favor of the standard member functions
added in C++20.

SPDX standardizes how source code conveys its copyright and licensing
information. See https://spdx.github.io/spdx-spec/1-rationale/ . SPDX
tags are adopted in many large projects, including things like the Linux
kernel.

Begins the transition to using fmt for string formatting where
applicable. Given fmt supports formatting std::string instances out of
the box, we can remove now-unnecessary calls to .c_str() and .data().

Note that this change does not touch the actual logging subsystem aside
from converting the final StringFromFormat call in the process over to
fmt::format. Given our logging system is heavily used throughout the
entire codebase, and converting that over will be quite a large change
by itself, this will be tackled near the end of the conversion process.