Complete DOMPluginEventSystem migration to createRoot

[eps1lon]

Follow-up to #28139 (comment)

I mistakenly kept the tests using comment nodes as containers as legacy tests. It's not that comments nodes aren't allowed in createRoot entirely. Only behind disableCommentsAsDOMContainers. We already had one test following that pattern so I just applied the same pattern to the other tests for consistency.

Now DOMPluginEventSystem no longer uses any legacy roots.

[react-sizebot]

Comparing: 971b62f...3dd7b56

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.min.js	=	176.59 kB	176.59 kB	=	55.01 kB	55.01 kB
oss-experimental/react-dom/cjs/react-dom.production.min.js	=	178.69 kB	178.69 kB	=	55.64 kB	55.64 kB
facebook-www/ReactDOM-prod.classic.js	=	573.52 kB	573.52 kB	=	100.99 kB	100.99 kB
facebook-www/ReactDOM-prod.modern.js	=	557.29 kB	557.29 kB	=	98.07 kB	98.07 kB
test_utils/ReactAllWarnings.js	Deleted	67.55 kB	0.00 kB	Deleted	16.54 kB	0.00 kB

Significant size changes

Includes any change greater than 0.2%:

Expand to show

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
test_utils/ReactAllWarnings.js	Deleted	67.55 kB	0.00 kB	Deleted	16.54 kB	0.00 kB

Generated by 🚫 dangerJS against 3dd7b56