Change FIXED_XDP from macros to constexprs #2575

Job	Run time
Check code formatting	41s
Check changelog formatting	5s
Get version info	22s
g2.dat	6s
macOS (x64) using CMake	6m 33s
Ubuntu Linux (noble, x86_64, portable)	10m 32s
Emscripten	14m 59s
macOS (arm64) using CMake	5m 18s
Debian Linux (bookworm, x86_64, portable)	9m 50s
Android	24m 45s
Ubuntu Linux (AppImage, x86_64)	8m 40s
Ubuntu Linux (debug) using clang, coverage enabled	12m 24s
Ubuntu Linux (Docker)	1s
Windows (win32)	8m 18s
Windows (win32) using mingw	8m 41s
Windows (x64)	9m 30s
Ubuntu Linux (noble, debug, [http, network, flac, vorbis OpenGL] disabled) using clang	8m 27s
Windows (arm64)	9m 45s
macOS universal app bundle	0s
Release	0s
	2h 18m 57s

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