Switching checked to null should leave the current value (#26667)

I accidentally made a behavior change in the refactor. It turns out that
when switching off `checked` to an uncontrolled component, we used to
revert to the concept of "initialChecked" which used to be stored on
state.

When there's a diff to this computed prop and the value of props.checked
is null, then we end up in a case where it sets `checked` to
`initialChecked`:

https:/facebook/react/blob/5cbe6258bc436b1683080a6d978c27849f1d9a22/packages/react-dom-bindings/src/client/ReactDOMInput.js#L69

Since we never changed `initialChecked` and it's not relevant if
non-null `checked` changes value, the only way this "change" could
trigger was if we move from having `checked` to having null.

This wasn't really consistent with how `value` works, where we instead
leave the current value in place regardless. So this is a "bug fix" that
changes `checked` to be consistent with `value` and just leave the
current value in place. This case should already have a warning in it
regardless since it's going from controlled to uncontrolled.

Related to that, there was also another issue observed in
facebook/react#26596 (comment) and
facebook/react#26588

We need to atomically apply mutations on radio buttons. I fixed this by
setting the name to empty before doing mutations to value/checked/type
in updateInput, and then set the name to whatever it should be. Setting
the name is what ends up atomically applying the changes.

---------

Co-authored-by: Sophie Alpert <[email protected]>

DiffTrain build for [1f248bdd7199979b050e4040ceecfe72dd977fd1](facebook/react@1f248bd)

compiled/facebook-www/REVISION

@@ -1 +1 @@
-c6db19f9cdec34bca3625a483a2f85181193b885
+1f248bdd7199979b050e4040ceecfe72dd977fd1

compiled/facebook-www/React-dev.modern.js

@@ -27,7 +27,7 @@ if (
 }
  "use strict";
 
-var ReactVersion = "18.3.0-www-modern-edf301ed";
+var ReactVersion = "18.3.0-www-modern-1cb1de96";
 
 // ATTENTION
 // When adding new symbols to this file,

compiled/facebook-www/ReactART-dev.classic.js

@@ -69,7 +69,7 @@ function _assertThisInitialized(self) {
  return self;
 }
 
-var ReactVersion = "18.3.0-www-classic-145c42eb";
+var ReactVersion = "18.3.0-www-classic-3f9bce70";
 
 var LegacyRoot = 0;
 var ConcurrentRoot = 1;

compiled/facebook-www/ReactART-prod.modern.js

@@ -9637,7 +9637,7 @@ var slice = Array.prototype.slice,
  return null;
  },
  bundleType: 0,
- version: "18.3.0-www-modern-294eaa58",
+ version: "18.3.0-www-modern-f1859984",
  rendererPackageName: "react-art"
  };
 var internals$jscomp$inline_1317 = {
@@ -9668,7 +9668,7 @@ var internals$jscomp$inline_1317 = {
  scheduleRoot: null,
  setRefreshHandler: null,
  getCurrentFiber: null,
- reconcilerVersion: "18.3.0-www-modern-294eaa58"
+ reconcilerVersion: "18.3.0-www-modern-f1859984"
 };
 if ("undefined" !== typeof __REACT_DEVTOOLS_GLOBAL_HOOK__) {
  var hook$jscomp$inline_1318 = __REACT_DEVTOOLS_GLOBAL_HOOK__;