[Blink] Ensure that CRP Create methods properly check for validity

[1] simplified CanvasRenderingContext2D for the fact that the various
CRP::Create*() methods have the conceptual invariant that they either
return a valid CRP or null. However, there turns out to be a bug in the
implementation of this invariant within CanvasResourceProvider:

* The CRP Create() methods call Clear() after they check IsValid() and
  before returning the provider.
* Clear() calls [FlushCanvas()][2].
* For accelerated raster, a FlushCanvas() call can impact the validity
  of the canvas due to detecting [GPU context loss][3]. e.g., we handle
  this possibility [here][4].

This CL adds checks of the provider's validity after the Clear() call
for the Create*() variants that use accelerated raster.

[1] https://chromium-review.googlesource.com/c/chromium/src/+/6811445
[2]: https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/renderer/platform/graphics/canvas_resource_provider.cc;l=2008;drc=e3ad182cacc3a02eb6a13091a867815fd17a129c
[3]: https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/renderer/platform/graphics/canvas_resource_provider.cc;l=290-293;drc=e3ad182cacc3a02eb6a13091a867815fd17a129c
[4]: https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/renderer/modules/canvas/canvas2d/canvas_rendering_context_2d.cc;l=310-316;drc=e3ad182cacc3a02eb6a13091a867815fd17a129c;bpv=1;bpt=1

Bug: 443234551, 352263194
Change-Id: Icba1d5ac87d7bbf50acf2ee56afc68d3b5781540
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6919400
Reviewed-by: Vasiliy Telezhnikov <vasilyt@chromium.org>
Commit-Queue: Colin Blundell <blundell@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1512257}