Implemented web image codec instantiation for CanvasKit.

[MichealReed]

Description

Network image did not work when using CanvasKit, this uses an http request to retrieve the image from the given uri and provides it to skia. Since this does not use an img tag, proper CORS handling will be required.

Related Issues

Fixes flutter/flutter#49725 and flutter/flutter#55476

Tests

Covered by existing tests.

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[Hixie]

This definitely needs tests.

[MOPineyro]

@MichealReed thanks for this PR, was hoping it would solve the issues, but still getting failures trying to load pngs with Network Image, any advice?

[yjbanov]

@MOPineyro please file a new issue so we can discuss it at the issue triage. It is also possible that you are hitting the CORS problem (flutter/flutter#45955), which is on our roadmap to address.