In certain cases, the platform can be "wayland-egl", "wayland-xcomposite", and other values for which I haven't found a full list yet. Instead of matching only "wayland", we now look for "wayland" anywhere in the `QT_QPA_PLATFORM` string in a case-insensitive manner.

Acknowledgements:
`CaseInsensitiveContains`' implementation was heavily inspired by GNU's non-standard glibc `strcasestr` function, which can be found here licensed under GPLv2 or later: https://ftp.gnu.org/gnu/libc/

With 12 uses of `JoinStrings` in the codebase vs 36 uses of `fmt::join`, fmtlib's range adapter for string concatenation with delimiters is clearly the preferred option.

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.