* add trailing commas on list/map/parameters
* add trailing commas on Invocation with nb of arg>1
* add commas for widget containing widgets
* add trailing commas if instantiation contains trailing comma
* revert bad change
## Description
This moves another 15-20ms from the animation jank of one of our important client to the startup latency. Unfortunately, this is probably not captured in our current benchmarks (presumably some other bottlenecks overshadow this shader compilation in the worst_frame benchmark). Considering that drawing images is such a common operation, maybe we should add one in the future to benchmark this.
We need this PR to land soon for our client because this changes the API to return Future.
## Related Issues
https://github.com/flutter/flutter/issues/813
This patch adds a default shader warm up process which moves shader compilation from the animation time to the startup time. This also provides an extension for `runApp` so developers can customize the warm up process.
This should reduce our worst_frame_rasterizer_time_millis from ~100ms to ~20-30ms for both flutter_gallery and complex_layout benchmarks. Besides, this should also have a significant improvement on 90th and 99th percentile time (50%-100% speedup in some cases, but I haven't tested them thoroughly; I'll let our device lab collect the data afterwards).
The tradeoff the is the startup time (time to first frame). Our `flutter run --profile --trace-startup` seems to be a little noisy and I see about 100ms-200ms increase in that measurement for complex_layout and flutter_gallery. Note that this only happens on the first run after install or data wipe. Later the Skia persistent cache will remove the overhead.
This also adds a cubic_bezier benchmark to test the custom shader warm up process.
This should fix https://github.com/flutter/flutter/issues/813 (either by `defaultShaderWarmUp`, or a `customShaderWarmUp`).
