Bug 1664459 - simplify WebRender radial gradient shader. r=mattwoodrow
Bug 1664459 - simplify WebRender radial gradient shader. r=mattwoodrow

Differential Revision: https://phabricator.services.mozilla.com/D89915

[ghsync] From https://hg.mozilla.org/mozilla-central/rev/83968b7074290fac064e9c88249814340dd3c708

servo/webrender,servo/webrender,servo/webrender,servo/webrender,servo/webrender,servo/webrender