[Impeller] Round out extreme angles between curve polyline segments.

[bdero]

Resolves flutter/flutter#137956.

Detect when the angle between two curve segments is > 10 degrees and insert smoothing geometry if so. See this comment for the full rationale behind this change.

    Paint paint = Paint()
      ..color = Colors.white
      ..strokeWidth = 50
      ..strokeCap = StrokeCap.round
      ..strokeJoin = StrokeJoin.round
      ..style = PaintingStyle.stroke;

    Path path = Path();
    path.moveTo(0, 0);
    path.quadraticBezierTo(100, 100, 0, 0);
    canvas.drawPath(path, paint);

Before:

After:

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Changes reported for pull request #53210 at sha 4aea5ec

[bdero]

Hmm, looks like this fix introduces a regression with CanRenderStrokePathThatEndsAtSharpTurn

[bdero]

5 degrees was way too sensitive a threshold. Bumped down to 10 degrees as it was attempting to smooth out pretty much everything.

[jonahwilliams]

LGTM!

[chinmaygarde]

This could perhaps go in //impeller/geometry.

[bdero]

Not opposed to throwing this in geometry. I'll do so in a follow-up. Also occurs to me that Ray is an inaccurate name for this... Should be something like SeparatedVector2.

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

Changes reported for pull request #53210 at sha 59adb6b