`src/debug_menu.cpp`: split functions from `void debug()` #87705

Job	Run time
matrix-variables	1s
skip-duplicates-code	4s
skip-duplicates-data	4s
Basic Build and Test (Clang 10, Ubuntu, Curses)	38m 38s
Clang 14, macOS 12, Tiles, Sound, x64 and arm64 Universal Binary	1h 30m 26s
GCC 9, Curses, LTO	53m 10s
Clang 12, Ubuntu, Tiles, ASan	2h 3m 52s
GCC 11, Ubuntu, Curses, ASan	2h 10m 37s
GCC 12, Ubuntu cross-compile to MinGW-Win64, Tiles, Sound	1h 6m 33s
GCC 9, Ubuntu, Tiles, Sound, CMake	17m 6s
	8h 40m 31s

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