Reconciler: Don't retry synchronous render

[eps1lon]

Summary

In https://github.com/facebook/react/pull/13041 we started retrying the render synchronously if a render threw during a concurrent render. However, this also applied to synchronous renders which should help very rarely since we don't support mutations during render. The original PR even explicitly said that a synchronous render should not be retried. We also didn't used to retry in legacy roots: https://react-error-recovery-showcase.vercel.app/

A lot of tests asserted on the retry even though their render was sync i.e. not wrapped in startTransition.

I originally caught this while investigating duplicate host instance creation in error boundary fallbacks. But this is expected by proxy of having error recovery for sync renders. Host instances are created during render phase.

How did you test this change?

• ~[ ] Codesandbox in https://github.com/facebook/react/issues/26518 no longer calls document.createElement twice~ We also create host instances twice when recovering from an error during concurrent render. We just never mutate the DOM twice. Creating host instances during render is intentional and documented
• Adjusted tests to not assert that sync render retries

[react-sizebot]

Comparing: 5b903cdaa94c78e8fabb985d8daca5bd7d266323...00d183b038af59f953cc12f444d562e5d463ef5c

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	+0.04%	497.54 kB	497.71 kB	+0.05%	88.93 kB	88.98 kB
oss-experimental/react-dom/cjs/react-dom.production.js	+0.03%	502.86 kB	503.04 kB	+0.05%	89.84 kB	89.88 kB
facebook-www/ReactDOM-prod.classic.js	+0.03%	591.00 kB	591.18 kB	+0.04%	103.95 kB	103.99 kB
facebook-www/ReactDOM-prod.modern.js	+0.03%	566.82 kB	566.99 kB	+0.06%	100.15 kB	100.21 kB
test_utils/ReactAllWarnings.js	Deleted	64.68 kB	0.00 kB	Deleted	16.15 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	64.68 kB	0.00 kB	Deleted	16.15 kB	0.00 kB

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