Add debug messages for corner_mask_cache

Log insertions in corner_mask_cache using GTK_NOTE with
GTK_DEBUG_MISC flag.
2 jobs for limit-corner-mask-cache in 9 minutes and 24 seconds (queued for 2 seconds)
latest
Status Job ID Name Coverage
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passed #172324
build

00:09:24

manual #172325
win32 allowed to fail manual
msys2-mingw32