[react-dom] Keep controlled <select> value on form reset

[eps1lon]

Closes #30580
Closes #34295

React's automatic form reset made it more apparent that controlled select is not working with form.reset(). Each form associated element has its own reset algorithm.

For <input>, that's reading back the value attribute which is why syncing the attribute value is critical for reset.

According to the spec, <select> reads from the selected attribute (https://html.spec.whatwg.org/multipage/form-elements.html#the-select-element) which is reflected from the defaultSelected DOM property. I adjusted the warning for setting selected via prop to make it clear why doing that is problematic.

Test plan

• selects DOM fixture is successful:
  • Desktop Chrome Version 143.0.7499.25
  • Desktop Firefox 145.0
  • Desktop Safari Version 18.6 (20621.3.11.11.3)
  • Mobile Android Chrome 142.0.7444.158
  • Mobile iOS Safari/Chrome (iPhone 17 air with iOS 26.0.1)
• (Waiting for CSB which is prob affected by CF outage but locally fixed) Original repro fixed with build from PR: https://codesandbox.io/p/devbox/react-controlled-select-subject-for-form-reset-forked-lhssfs?file=%2Fsrc%2Findex.js&workspaceId=ws_NXrhLjqHgWvFjhiKcfVFu6

[react-sizebot]

Comparing: 0972e23...cacd6ba

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	=	1.83 kB	1.83 kB
oss-stable/react-dom/cjs/react-dom-client.production.js	+0.03%	608.16 kB	608.32 kB	+0.03%	107.65 kB	107.68 kB
oss-experimental/react-dom/cjs/react-dom.production.js	=	6.69 kB	6.69 kB	=	1.83 kB	1.83 kB
oss-experimental/react-dom/cjs/react-dom-client.production.js	+0.02%	666.18 kB	666.34 kB	+0.03%	117.35 kB	117.39 kB
facebook-www/ReactDOM-prod.classic.js	+0.02%	693.31 kB	693.47 kB	+0.03%	121.98 kB	122.01 kB
facebook-www/ReactDOM-prod.modern.js	+0.02%	683.73 kB	683.90 kB	+0.03%	120.36 kB	120.40 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	+0.22%	66.51 kB	66.66 kB	+0.12%	16.74 kB	16.76 kB

Generated by 🚫 dangerJS against cacd6ba

[billyjanitsch]

@eps1lon thanks for this PR. I'm glad to see this fixed!

Checkboxes and radio inputs are also affected. (See #31695.) Would it be straightforward to fix them in the same way?

[eps1lon]

I'll follow-up with that once this is merged.