[Fizz] Outline if a boundary would add too many bytes to the next completion

[sebmarkbage]

Follow up to #33027.

This enhances the heuristic so that we accumulate the size of the currently written boundaries. Starting from the size of the root (minus preamble) for the shell.

This ensures that if you have many small boundaries they don't all continue to get inlined. For example, you can wrap each paragraph in a document in a Suspense boundary to regain document streaming capabilities if that's what you want.

However, one consideration is if it's worth producing a fallback at all. Maybe if it's like null it's free but if it's like a whole alternative page, then it's not. It's possible to have completely useless Suspense boundaries such as when you nest several directly inside each other. So this uses a limit of at least 500 bytes of the content itself for it to be worth outlining at all. It also can't be too small because then for example a long list of paragraphs can never be outlined.

In the fixture I straddle this limit so some paragraphs are too small to be considered. An unfortunate effect of that is that you can end up with some of them not being outlined which means that they appear out of order. SuspenseList is supposed to address that but it's unfortunate.

The limit is still fairly high though so it's unlikely that by default you'd start outlining anything within the viewport at all. I had to reduce the progressiveChunkSize by an order of magnitude in my fixture to try it out properly.

[react-sizebot]

Comparing: 8e9a5fc...8703f8a

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	=	527.72 kB	527.72 kB	=	93.07 kB	93.07 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	=	633.34 kB	633.34 kB	=	111.25 kB	111.25 kB
facebook-www/ReactDOM-prod.classic.js	=	671.13 kB	671.13 kB	=	117.70 kB	117.70 kB
facebook-www/ReactDOM-prod.modern.js	=	661.41 kB	661.41 kB	=	116.14 kB	116.14 kB

Significant size changes

Includes any change greater than 0.2%:

(No significant changes)

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