Bug 2029028 - Enable Servo support for background-blend-mode. r=firefox-style-system-reviewers,emilio

Imports servo/stylo#344

Differential Revision: https://phabricator.services.mozilla.com/D291915

Author: mrobinson

servo/components/style/properties/longhands.toml

@@ -3535,11 +3535,11 @@ keyword = { values = ["padding-box", "border-box", "content-box"], gecko_enum_pr
 
 [background-blend-mode]
 struct = "background"
-engine = "gecko"
 vector = {}
 animation_type = "discrete"
 spec = "https://drafts.fxtf.org/compositing/#background-blend-mode"
 affects = "paint"
+servo_restyle_damage = "repaint"
 
 [background-blend-mode.keyword]
 values = [