Add doctype to renderToMarkup when html tags are rendered

[sebmarkbage]

Stacked on top of #30121.

This is the same thing we do for renderToReadableStream so that you don't have to manually inject it into the stream.

The only reason we didn't for renderToString / renderToStaticMarkup was to preserve legacy behavior but since this is a new API we can change that.

If you're rendering a partial it doesn't matter. This is likely what you'd do for RSS feeds. The question is if you can reliably rely on the doctype being used while rendering e-mails since many clients are so quirky. However, if you're careful it also doesn't hurt so it seems best to include it.

[vercel]

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Name	Status	Preview	Comments	Updated (UTC)
react-compiler-playground	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Jun 28, 2024 1:28pm

[react-sizebot]

Comparing: 1e241f9...77832d9

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	+0.05%	1.83 kB	1.83 kB
oss-stable/react-dom/cjs/react-dom-client.production.js	=	497.99 kB	497.99 kB	=	89.27 kB	89.27 kB
oss-experimental/react-dom/cjs/react-dom.production.js	=	6.69 kB	6.69 kB	+0.05%	1.83 kB	1.83 kB
oss-experimental/react-dom/cjs/react-dom-client.production.js	=	502.81 kB	502.81 kB	=	89.97 kB	89.97 kB
facebook-www/ReactDOM-prod.classic.js	=	597.08 kB	597.08 kB	=	105.33 kB	105.34 kB
facebook-www/ReactDOM-prod.modern.js	=	571.42 kB	571.42 kB	=	101.27 kB	101.27 kB
test_utils/ReactAllWarnings.js	Deleted	62.88 kB	0.00 kB	Deleted	15.69 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	62.88 kB	0.00 kB	Deleted	15.69 kB	0.00 kB

Generated by 🚫 dangerJS against 77832d9