Changes in 20210103092941

Built from 1098ab162ad2352f7623193c1bbb80834d0b5d3a

..index..
Bug 1684673 N[Core:CSS Parsing and Computation]Some minor tweaks to class attribute handling.
Bug 1684689 U[Core:Canvas: 2D]WPT test fails for html/canvas/element/pixel-manipulation/2d.imageData.create2.zero.html
Bug 1664730 A[Core:DOM: UI Events & Focus Handling]Intermittent toolkit/content/tests/mochitest/test_mousecapture.xhtml | selection scroll position after timer is at least 140
Bug 1684668 R[Core:GFX: Color Management]Rename in_0 to input and out to output.
Bug 1684691 R[Core:GFX: Color Management]Make Matrix more Rust like.
Bug 1684696 R[Core:GFX: Color Management]Use a more Rust like style in a bunch of places.
Bug 987432 R[Core:SVG]Clean up possibly-unnecessary float casts in SVG matrix-creation code (maybe just replacing with gfx::Float)
Bug 1684645 R[Firefox Build System:Generated Documentation]Regex for copybutton_prompt_text not working
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Changes to 8 bugs - 5 fixed.