core/renderloop: log frame statistics into a file
Data like target vs. actual pageflip time, and render times is often needed for debugging or optimizing render time predictions, so this commit makes KWin print that information to a file in the home directory whenever KWIN_LOG_PERFORMANCE_DATA is set.
(cherry picked from commit a169114f)
Co-authored-by: Xaver Hugl xaver.hugl@gmail.com