[Fiber] Double invoke Effects in StrictMode after Fast Refresh

[eps1lon]

Summary

Fixes #29915

Ensures Effects are also double invoked when a Component newly mounts due to Fast Refresh. Looks to have been an oversight in the remountFiber path.

How did you test this change?

• Added test (see first commit for previous behavior)

[react-sizebot]

Comparing: 23fcd7c...1eab7a6

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	=	6.84 kB	6.84 kB	=	1.88 kB	1.88 kB
oss-stable/react-dom/cjs/react-dom-client.production.js	=	612.91 kB	612.91 kB	=	108.30 kB	108.30 kB
oss-experimental/react-dom/cjs/react-dom.production.js	=	6.84 kB	6.84 kB	+0.05%	1.88 kB	1.88 kB
oss-experimental/react-dom/cjs/react-dom-client.production.js	=	678.85 kB	678.85 kB	=	119.27 kB	119.27 kB
facebook-www/ReactDOM-prod.classic.js	=	698.58 kB	698.58 kB	=	122.74 kB	122.74 kB
facebook-www/ReactDOM-prod.modern.js	=	688.90 kB	688.90 kB	=	121.12 kB	121.12 kB

Significant size changes

Includes any change greater than 0.2%:

(No significant changes)

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