[web] Fix some clip and stroke calculations

[mdebbar]

When an element is drawn with a stroke paint, we correctly bake stroke width into the transform calculations. But if the the element is clipped, the transform is recalculated without the stroke width math.

This PR makes sure that the stroke width adjustments are carried over to the clip calculations.

Fixes flutter/flutter#76879

I added new screenshot tests, here's what they look like before and after the fix:

	Before	After
Rect
RRect
Circle

[skia-gold]

Gold has detected about 1 new digest(s) on patchset 2.
View them at https://flutter-engine-gold.skia.org/cl/github/36801

[yjbanov]

Could we remove both of the if blocks below, if we did the following ahead of time?

if (paint.style == ui.PaintingStyle.fill || strokeWidth == 0.0) {
  return rect;
}

[mdebbar]

Unfortunately, we can't.

Stroke-related adjustments aren't the only ones needed. We need to also adjust left and top to avoid flipped rectangles.

E.g. Rect.fromLTRB(200, 200, 100, 100) is completely fine in Flutter, but the DOM doesn't like it. If you do rect.width on a flipped rectangle, you get a negative value. Setting a negative width/height on a DOM element is equivalent to zero.

buildDrawRectElement and various draw operations used to handle it. See this:

engine/lib/web_ui/lib/src/engine/html/dom_canvas.dart

Lines 175 to 178 in 2ced979

	final double left = math.min(rect.left, rect.right);
	final double right = math.max(rect.left, rect.right);
	final double top = math.min(rect.top, rect.bottom);
	final double bottom = math.max(rect.top, rect.bottom);

and:

engine/lib/web_ui/lib/src/engine/html/bitmap_canvas.dart

Lines 445 to 449 in 2ced979

	_drawElement(
	element,
	ui.Offset(
	math.min(rect.left, rect.right), math.min(rect.top, rect.bottom)),
	paint);

All of that can go away now because rects produced by the new adjustRectForDom are never flipped.

[skia-gold]

Gold has detected about 2 new digest(s) on patchset 2.
View them at https://flutter-engine-gold.skia.org/cl/github/36801

[skia-gold]

Gold has detected about 3 new digest(s) on patchset 3.
View them at https://flutter-engine-gold.skia.org/cl/github/36801

[harryterkelsen]

LGTM

[skia-gold]

Gold has detected about 3 new digest(s) on patchset 5.
View them at https://flutter-engine-gold.skia.org/cl/github/36801

[skia-gold]

Gold has detected about 4 new digest(s) on patchset 7.
View them at https://flutter-engine-gold.skia.org/cl/github/36801