Every module unit now includes the standard headers it uses. Declarations
reaching a unit only through an imported module's global module fragment
are reachable but not visible, so ADL misses the free operators older
libstdc++ declares beside a type - reproduced on ubuntu 24.04 (libstdc++
13), where gl/vao.cpp could not compare vector iterators.
Also drops a stale editor/editorSettings.hpp from the MSVC source list,
which broke the Windows configure step, silences the deliberate
include-in-purview warning in the glm wrapper, and removes GCC support:
clang or MSVC only.
Consolidates platform-specific config-directory logic (APPDATA on Windows,
~/Library/Application Support on macOS, ~/.config on Linux) into a single
user_config_path(filename) function in utilities/utilities.{cpp,h}, removing
copy-pasted #ifdef blocks from application.cpp, editor/editorSettings.cpp,
input/{keyboard,gamepad,drivermouse,uart}input.cpp.
