Fix: Activity should hide portal contents (#35091)

This PR updates the behavior of Activity so that when it is hidden, it
hides the contents of any portals contained within it.

Previously we had intentionally chosen not to implement this behavior,
because it was thought that this concern should be left to the userspace
code that manages the portal, e.g. by adding or removing the portal
container from the DOM. Depending on the use case for the portal, this
is often desirable anyway because the portal container itself is not
controlled by React.

However, React does own the _contents_ of the portal, and we can hide
those elements regardless of what the user chooses to do with the
container. This makes the hiding/unhiding behavior of portals with
Activity automatic in the majority of cases, and also benefits from
aligning the DOM mutations with the rest of the React's commit phase
lifecycle.

The reason we have to special case this at all is because usually we
only hide the direct DOM children of the Activity boundary. There's no
reason to go deeper than that, because hiding a parent DOM element
effectively hides everything inside of it. Portals are the exception,
because they don't exist in the normal DOM hierarchy; we can't assume
that just because a portal has a parent in the React tree that it will
also have that parent in the actual DOM.

So, whenever an Activity boundary is hidden, we must search for and hide
_any_ portal that is contained within it, and recursively hide its
direct children, too.

To optimize this search, we use a new subtree flag, PortalStatic, that
is set only on fiber paths that contain a HostPortal. This lets us skip
over any subtree that does not contain a portal.

DiffTrain build for [5268492](5268492)

Author: acdlite

compiled/facebook-www/REVISION

@@ -1 +1 @@
-c83be7da9f0861770d7df52842d1c3dfe60f0927
+52684925368a41a0c9fbfca9016cdcbb72fc9d1e

compiled/facebook-www/REVISION_TRANSFORMS

@@ -1 +1 @@
-c83be7da9f0861770d7df52842d1c3dfe60f0927
+52684925368a41a0c9fbfca9016cdcbb72fc9d1e

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

@@ -1499,7 +1499,7 @@ __DEV__ &&
     exports.useTransition = function () {
       return resolveDispatcher().useTransition();
     };
-    exports.version = "19.3.0-www-classic-c83be7da-20251109";
+    exports.version = "19.3.0-www-classic-52684925-20251110";
     "undefined" !== typeof __REACT_DEVTOOLS_GLOBAL_HOOK__ &&
       "function" ===
         typeof __REACT_DEVTOOLS_GLOBAL_HOOK__.registerInternalModuleStop &&

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

@@ -1499,7 +1499,7 @@ __DEV__ &&
     exports.useTransition = function () {
       return resolveDispatcher().useTransition();
     };
-    exports.version = "19.3.0-www-modern-c83be7da-20251109";
+    exports.version = "19.3.0-www-modern-52684925-20251110";
     "undefined" !== typeof __REACT_DEVTOOLS_GLOBAL_HOOK__ &&
       "function" ===
         typeof __REACT_DEVTOOLS_GLOBAL_HOOK__.registerInternalModuleStop &&

compiled/facebook-www/React-prod.classic.js

@@ -606,4 +606,4 @@ exports.useSyncExternalStore = function (
 exports.useTransition = function () {
   return ReactSharedInternals.H.useTransition();
 };
-exports.version = "19.3.0-www-classic-c83be7da-20251109";
+exports.version = "19.3.0-www-classic-52684925-20251110";

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

@@ -606,4 +606,4 @@ exports.useSyncExternalStore = function (
 exports.useTransition = function () {
   return ReactSharedInternals.H.useTransition();
 };
-exports.version = "19.3.0-www-modern-c83be7da-20251109";
+exports.version = "19.3.0-www-modern-52684925-20251110";

compiled/facebook-www/React-profiling.classic.js

@@ -610,7 +610,7 @@ exports.useSyncExternalStore = function (
 exports.useTransition = function () {
   return ReactSharedInternals.H.useTransition();
 };
-exports.version = "19.3.0-www-classic-c83be7da-20251109";
+exports.version = "19.3.0-www-classic-52684925-20251110";
 "undefined" !== typeof __REACT_DEVTOOLS_GLOBAL_HOOK__ &&
   "function" ===
     typeof __REACT_DEVTOOLS_GLOBAL_HOOK__.registerInternalModuleStop &&

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

@@ -610,7 +610,7 @@ exports.useSyncExternalStore = function (
 exports.useTransition = function () {
   return ReactSharedInternals.H.useTransition();
 };
-exports.version = "19.3.0-www-modern-c83be7da-20251109";
+exports.version = "19.3.0-www-modern-52684925-20251110";
 "undefined" !== typeof __REACT_DEVTOOLS_GLOBAL_HOOK__ &&
   "function" ===
     typeof __REACT_DEVTOOLS_GLOBAL_HOOK__.registerInternalModuleStop &&