Create DlCanvas interface and implement with DisplayListBuilder and SkCanvasAdapter

[flar]

Fixes: flutter/flutter#109578

This PR introduces a new DlCanvas interface which will be the only interface used for rendering moving forward.

With the changes here, nearly all code in the engine is moved off of SkCanvas/SkPaint onto DlCanvas/DlPaint with some exceptions for platform code and for code which was already using DisplayListBuilder instead. Moving everything From DisplayListBuilder onto DlCanvas will be a follow-on task.

These changes are consistent with a new direction for the DL source code organization. The new code follows a hierarchical code tree under flutter/display_list/ and new files are named dl_... instead of display_list_.... Old code is left using the flat hierarchy with the old file naming for now, but a mass change may be coming before too long to get all of the code to conform. Also, the intent is that DlCanvas will follow Flutter style guidelines rather than Skia-like style, but the rest of the files will remain Skia-ish and converge over time.

The code is compiling on a Mac for host, iOS and Android and most unit tests pass on that host (and a brief test on Linux).

[chinmaygarde]

Besides just the sheer number of lines of code touched, the patch looks relatively safe and only modifies internal interfaces. I expect a few more patches of this nature as we cleanup the internals after the display list migration. Is this a draft only till we fix the Fuchsia interfaces or is anything else remaining? Its best not to sit on this for too long and let the conflicts pile up.

[flar]

Mainly a draft because I didn't know how many failures I'd see during CI, but now that it is down to just a couple, I'll "undraft" it...

[flar]

I've narrowed down the test failure to a side effect of a recent optimization. I can comment out FlutterPlatformViews.mm line 801 (a ClipRect when rendering embedder slice content over the embedder layer) and the test passes, but that would eliminate the recently added optimization.

@cyanglaz any thoughts?

[flar]

While @chinmaygarde has already approved this (pending fixing the last test failure), I'd like to call attention to other engineers who work on the DL and related systems a bit... @JsouLiang @ColdPaleLight @bdero @jason-simmons

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Changes reported for pull request #39762 at sha 4f2533a

[flar]

I believe I have the final piece of the puzzle. The android embedder failures appear to be due to the way we record setTransform in DisplayList objects and play them back into SkCanvas compared to the way that used to be done by SkPicture. If I comment out all of the calls to "integralTransform" which is the only place we use setTransform, things show up fine. I need more investigation, but I think SkPicture treats a setTransform as "set the transform back to what it was before drawPicture was called", but our DL dispatcher sets it to identity.

Yes, this appears to be the case:
https://skia.googlesource.com/skia/+/refs/heads/main/src/core/SkPicturePlayback.cpp#50
and:
https://skia.googlesource.com/skia/+/refs/heads/main/src/core/SkPicturePlayback.cpp#694