CanvasKit fix embedded view clipping

[harryterkelsen]

Description

Fixes embedded view clipping by using html.DocumentFragment.svg to avoid the problem where the clipPath elements were automatically lower-cased.

Related Issues

Fixes flutter/flutter#70618

Tests

I added the following tests:

• Added a test to embedded_views_test that clipPath is correctly added to the DOM.

Checklist

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• I read the contributor guide and followed the process outlined there for submitting PRs.
• I signed the CLA.
• I read and followed the C++, Objective-C, Java style guides for the engine.
• I read the tree hygiene wiki page, which explains my responsibilities.
• I updated/added relevant documentation.
• All existing and new tests are passing.
• I am willing to follow-up on review comments in a timely manner.

Reviewer Checklist

• I have submitted any presubmit flakes in this PR using the engine presubmit flakes form before re-triggering the failure.

Breaking Change

Did any tests fail when you ran them? Please read handling breaking changes.

• No, no existing tests failed, so this is not a breaking change.
• Yes, this is a breaking change.

[yjbanov]