Since `WP_Image_Editor`'s introduction, stream wrappers have functioned in `WP_Image_Editor_GD`, but haven't been properly supported in `WP_Image_Editor_Imagick`.
- Detects stream wrappers and uses `file_put_contents()` along with `Imagick::read/getImageBlob()` for handling when necessary.
- Introduces private method, `WP_Image_Editor_Imagick::write_image` to handle detection and proper saving.
- Introduces `WP_Test_Stream` class for testing stream wrappers, along with new tests for Imagick's stream handling and a stream filename test.
Adds requirement for `Imagick::readImageBlob()`, available in Imagick >= 2.0.0, which aligns with the current requirement of Imagick >= 2.2.0.
Props p00ya, calin, joemcgill, pputzer, jimyaghi, mikeschroder.
Fixes#42663.
git-svn-id: https://develop.svn.wordpress.org/trunk@49230 602fd350-edb4-49c9-b593-d223f7449a82
Mike Schroder