[css-paint-api] Add CanvasFilters to PaintRenderingContext2D

[bfgeek]

This was an oversight on my behalf, and was brought up as part of exposing more 2D canvas APIs.
#1055

Blink's implementation has had this since we shipped (and tests).

[Kaiido]

I guess that would fix #1022

[css-meeting-bot]

The CSS Working Group just discussed [css-paint-api] Add CanvasFilters to PaintRenderingContext2D, and agreed to the following:

• RESOLVED: Add CanvasFilter to PaintRenderingContext2D

The full IRC log of that discussion

<fantasai> Topic: [css-paint-api] Add CanvasFilters to PaintRenderingContext2D
<fantasai> github: https://github.com//issues/1056
<fantasai> iank_: PaintREnderingContext2D implemented subset of CanvasRenderingContext2D
<fantasai> iank_: removed things that don't make sense in a paint worklet, e.g. dom apis and text
<fantasai> iank_: One oversight, probably mine, was that we didn't add the CanvasFilters APIs
<fantasai> iank_: allows to set e.g. filter blur 2px
<fantasai> iank_: We've been shipping this, people have been using it
<fantasai> iank_: it's part of CanvasREnderingContext2D standard
<fantasai> iank_: so just want to add this interface to PaintRenderingContext2D
<fantasai> astearns: Any concerns with adding CanvasFilters?
<fantasai> astearns: There are other implementations of Paint API?
<fantasai> iank_: Only prototype implementations
<fantasai> iank_: so I believe that WebKit at one point had a protype implementation, also one in servo
<fantasai> iank_: but that obviously not moving forward atm
<fantasai> iank_: we're the only folks shipping atm
<fantasai> astearns: Might wait for smfr's input, but I'm OK adding to spec and if necessary reopen issue
<TabAtkins> +1
<flackr> +1
<fantasai> fantasai: sgtm
<fantasai> RESOLVED: Add CanvasFilter to PaintRenderingContext2D
<TabAtkins> ScribeNick: TabAtkins
<TabAtkins> Issue: listifying border color
<TabAtkins> github:
<TabAtkins> github: https://github.com//issues/1056