Add stats per function call to Function Chart (GUI)

[jkunstwald]

• Add per-call min, max, average and std dev times to the function chart window
  • Values min/maxed/avgd across calls, not frames, unlike the existing ones
• Clarified the tooltips for the existing averages ("Average Time" -> "Time spent in this function during an average frame")
• Precompute all these stats including the existing AvgTotal, AvgWait, AvgWork during load instead of in the getters

Not sure if this is a good idea or if you want the values to be somewhere else, i required this feature personally. The performance impact is minimal now that the values are precomputed, in fact this is likely a flat improvement over the current version even though more things are computed