[Impeller] Add direct tesselation of circles for DrawCircle and Round end caps

[flar]

Note: The GPU tesselation for drawPoints is disabled in this test PR, but will be re-enabled when I can run some benchmarks to see where a good cutoff exists.

Tessellation for circular or quarter circular paths is now handled by a single tessellator class that provides services for DrawCircle, DrawPoints (round caps), and DrawLines (round caps). Creating a general path is avoided along with the associated overhead of recognizing and using a generic tessellation step.

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Changes reported for pull request #48103 at sha fbe91b4

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Changes reported for pull request #48103 at sha 92b97fd

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Golden file changes are available for triage from new commit, Click here to view.

Changes reported for pull request #48103 at sha 39f8a54

[flar]

I triaged the new golden for the brand new test created here, but left all of the others for others to look. We don't tessellate the circles exactly the same as the Path might have done it, instead now using the same technique that had been used in DrawPoints(PointMode), but hopefully with very similar fidelity. I wanted to leave those golden diffs un-triaged so that reviewers could look through them and evaluate any fidelity differences.

[flar]

Here are 2 charts that demonstrate the performance of the new direct tessellation code to the previous mechanisms.

Note that the regressions in DrawPoints(PointMode) are due to the measurements being taken with the special point_field GPU tessellator disabled for comparison purposes. In other words, this comparison for PointMode demonstrates that the custom CPU tessellator is not much slower than the GPU tessellator even at 10k points being processed. The GPU tessellator is still used at the same performance levels, I just disabled it for testing and benchmarking these numbers.

DrawLine and DrawPoints on Pixel 6a

DrawLine and DrawPoints on M1 MBPro

[flar]

I will be looking at doing HostBuffer emplacement for PointField geometry as well. Not sure if I should do it now, or as a follow-on PR...

[flar]

I reran the 10k line/point benchmarks again with the direct HostBuffer emplacement - all except the PointMode measurements since those continue to use GPU in the latest commit and so they haven't changed. The direct HostBuffer emplacement had a small but measurable improvement over the vertex builders.

The blue lines are prior to these changes and the red/orange lines are with these changes. The orange line improves over the red line due to the HostBuffer emplacement technique.

DrawLine and DrawPoints on Pixel 6a

DrawLine and DrawPoints on M1 MBPro

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Golden file changes are available for triage from new commit, Click here to view.

Changes reported for pull request #48103 at sha 769d4af

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Golden file changes are available for triage from new commit, Click here to view.

Changes reported for pull request #48103 at sha 4ccdb46

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Changes reported for pull request #48103 at sha aeef542

[flar]

This should be in its (hopefully) final form ready for review.

I left the goldens untriaged for review, but I've done a cursory inspection and they look like the kind of diffs one would expect for the change in the math.

[jonahwilliams]

LGTM with nit

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Changes reported for pull request #48103 at sha 16fa52d

[jonahwilliams]

Nice improvements on draw circle: https://flutter-engine-perf.skia.org/e/?queries=test%3DBM_CanvasRecord_draw_circle&selected=commit%3D38393%26name%3D%252Cconfig%253Ddefault%252Ccpu_scaling_enabled%253Dfalse%252Cexecutable%253D_b_s_w_ir_cache_builder_src_out_host_release_canvas_benchmarks%252Clibrary_build_type%253Drelease%252Cmhz_per_cpu%253D2200%252Cnum_cpus%253D8%252Csub_result%253DTotalOpCount%252Ctest%253DBM_CanvasRecord_draw_circle%252Cunit%253Dns%252C