Add DOM fixture page for Fragment Ref

[jackpope]

This adds a page to the DOM fixture to test Fragment Refs. The first test case is for addEventListener/removeEventListener.

Setting enableFragmentRefs to __EXPERIMENTAL__ and building is required to run the fixture.

[react-sizebot]

Comparing: 75c9798...e443463

Critical size changes

Includes critical production bundles, as well as any change greater than 2%:

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
oss-stable/react-dom/cjs/react-dom.production.js	=	6.68 kB	6.68 kB	=	1.83 kB	1.83 kB
oss-stable/react-dom/cjs/react-dom-client.production.js	=	518.75 kB	518.75 kB	=	92.47 kB	92.47 kB
oss-experimental/react-dom/cjs/react-dom.production.js	=	6.69 kB	6.69 kB	=	1.83 kB	1.83 kB
oss-experimental/react-dom/cjs/react-dom-client.production.js	=	591.76 kB	591.66 kB	=	105.36 kB	105.33 kB
facebook-www/ReactDOM-prod.classic.js	=	652.39 kB	652.39 kB	=	114.72 kB	114.72 kB
facebook-www/ReactDOM-prod.modern.js	=	642.71 kB	642.71 kB	=	113.15 kB	113.15 kB

Significant size changes

Includes any change greater than 0.2%:

(No significant changes)

Generated by 🚫 dangerJS against 7389b72