Convert ReactMount to createRoot (#28075)

To convert this file, I started replacing all the calls in line, and
quickly realized that we already have most of these tests covered in
other files. So I found the test that we didn't already have for
`create/hydrateRoot` and added them, then renamed `ReactMount` to
`ReactLegacyMount`.

DiffTrain build for commit https://github.com/facebook/react/commit/5420c4ea08a4ccf06b04f0c0abdf1f5e8d84223a.

compiled-rn/facebook-fbsource/xplat/js/RKJSModules/vendor/react-test-renderer/cjs/ReactTestRenderer-dev.js

@@ -25572,7 +25572,7 @@ if (__DEV__) {
       return root;
     }
 
-    var ReactVersion = "18.3.0-canary-11c9fd0c5-20240124";
+    var ReactVersion = "18.3.0-canary-5420c4ea0-20240124";
 
     // Might add PROFILE later.
 

compiled-rn/facebook-fbsource/xplat/js/RKJSModules/vendor/react-test-renderer/cjs/ReactTestRenderer-prod.js

@@ -9131,7 +9131,7 @@ var devToolsConfig$jscomp$inline_1031 = {
     throw Error("TestRenderer does not support findFiberByHostInstance()");
   },
   bundleType: 0,
-  version: "18.3.0-canary-11c9fd0c5-20240124",
+  version: "18.3.0-canary-5420c4ea0-20240124",
   rendererPackageName: "react-test-renderer"
 };
 var internals$jscomp$inline_1207 = {
@@ -9162,7 +9162,7 @@ var internals$jscomp$inline_1207 = {
   scheduleRoot: null,
   setRefreshHandler: null,
   getCurrentFiber: null,
-  reconcilerVersion: "18.3.0-canary-11c9fd0c5-20240124"
+  reconcilerVersion: "18.3.0-canary-5420c4ea0-20240124"
 };
 if ("undefined" !== typeof __REACT_DEVTOOLS_GLOBAL_HOOK__) {
   var hook$jscomp$inline_1208 = __REACT_DEVTOOLS_GLOBAL_HOOK__;

compiled-rn/facebook-fbsource/xplat/js/RKJSModules/vendor/react-test-renderer/cjs/ReactTestRenderer-profiling.js

@@ -9559,7 +9559,7 @@ var devToolsConfig$jscomp$inline_1073 = {
     throw Error("TestRenderer does not support findFiberByHostInstance()");
   },
   bundleType: 0,
-  version: "18.3.0-canary-11c9fd0c5-20240124",
+  version: "18.3.0-canary-5420c4ea0-20240124",
   rendererPackageName: "react-test-renderer"
 };
 var internals$jscomp$inline_1248 = {
@@ -9590,7 +9590,7 @@ var internals$jscomp$inline_1248 = {
   scheduleRoot: null,
   setRefreshHandler: null,
   getCurrentFiber: null,
-  reconcilerVersion: "18.3.0-canary-11c9fd0c5-20240124"
+  reconcilerVersion: "18.3.0-canary-5420c4ea0-20240124"
 };
 if ("undefined" !== typeof __REACT_DEVTOOLS_GLOBAL_HOOK__) {
   var hook$jscomp$inline_1249 = __REACT_DEVTOOLS_GLOBAL_HOOK__;

compiled-rn/facebook-fbsource/xplat/js/RKJSModules/vendor/react/cjs/React-dev.js

@@ -24,7 +24,7 @@ if (__DEV__) {
     ) {
       __REACT_DEVTOOLS_GLOBAL_HOOK__.registerInternalModuleStart(new Error());
     }
-    var ReactVersion = "18.3.0-canary-11c9fd0c5-20240124";
+    var ReactVersion = "18.3.0-canary-5420c4ea0-20240124";
 
     // ATTENTION
     // When adding new symbols to this file,

compiled-rn/facebook-fbsource/xplat/js/RKJSModules/vendor/react/cjs/React-prod.js

@@ -539,4 +539,4 @@ exports.useSyncExternalStore = function (
 exports.useTransition = function () {
   return ReactCurrentDispatcher.current.useTransition();
 };
-exports.version = "18.3.0-canary-11c9fd0c5-20240124";
+exports.version = "18.3.0-canary-5420c4ea0-20240124";

compiled-rn/facebook-fbsource/xplat/js/RKJSModules/vendor/react/cjs/React-profiling.js

@@ -535,7 +535,7 @@ exports.useSyncExternalStore = function (
 exports.useTransition = function () {
   return ReactCurrentDispatcher.current.useTransition();
 };
-exports.version = "18.3.0-canary-11c9fd0c5-20240124";
+exports.version = "18.3.0-canary-5420c4ea0-20240124";
 "undefined" !== typeof __REACT_DEVTOOLS_GLOBAL_HOOK__ &&
   "function" ===
     typeof __REACT_DEVTOOLS_GLOBAL_HOOK__.registerInternalModuleStop &&

compiled-rn/facebook-fbsource/xplat/js/react-native-github/Libraries/Renderer/REVISION

@@ -1 +1 @@
-11c9fd0c53133f24f5270d36591b65b8fc2ebd25
+5420c4ea08a4ccf06b04f0c0abdf1f5e8d84223a