Status Chart: Avoid emitting consecutive zeros

[StephanTLavavej]

• Avoid emitting consecutive zeros.
  • Now that we've finished C++20, the cxx20 line is constantly zero. I want it to simply vanish, as the C++17 line did (which was manually recorded in weekly_table.js, so we just stopped recording data points). To do this in a general way, I'm splitting the daily table generation into two phases. First, we calculate all of the data points (this part takes a bit of time, so there's a progress bar). Then, we determine which data points should be kept - this requires looking at the previous and next values, so it has to be a separate phase. should_emit_data_point() will keep a value if it's nonzero (which we definitely need!), if the previous value exists and was nonzero (because when we fall to zero, we want to record a single zero before stopping), or if the next value exists and will be nonzero (to properly display liftoff from zero).
  • The optional chaining operator ?. makes this look very nice because the bounds checks are implicit. In rows[i - 1]?.[key] > 0, when i === 0, then rows[i - 1] will be undefined; the optional chaining operator will short-circuit instead of attempting to access the [key] (which would otherwise be an error) and return undefined. Then undefined > 0 is false, which is what we want - at the beginning of the dataset, there is no previous value to consider, so we'll consider only the current and next data point.
  • This also allows us to drop the hardcoded begin_cxx23.
• npm update.
• weekly_table.js: 2021-04-30 update.
• Adjust PR Age max and stepSize.
• Update usernames_contributors.txt.
• chart.js 3.2.1.

📉 Live preview: stephantlavavej.github.io/STL/

Note: To avoid merge conflicts, this doesn't update daily_table.js, thus the effect of dropping zeros can't be seen yet. It affects the beginning of the bug line, and the end of the cxx20 line.