Clean up experimental flags (#28116)

## Overview

Adds a new global to disambiguate experimental flags that we intend to
land when we can make breaking changes.

packages/shared/ReactFeatureFlags.js

@@ -129,6 +129,41 @@ export const retryLaneExpirationMs = 5000;
 export const syncLaneExpirationMs = 250;
 export const transitionLaneExpirationMs = 5000;
 
+// -----------------------------------------------------------------------------
+// Ready for next major.
+//
+// Alias __NEXT_MAJOR__ to __EXPERIMENTAL__ for easier skimming.
+// -----------------------------------------------------------------------------
+const __NEXT_MAJOR__ = __EXPERIMENTAL__;
+
+// Not ready to break experimental yet.
+export const disableLegacyContext = false;
+
+// Not ready to break experimental yet.
+// Disable javascript: URL strings in href for XSS protection.
+export const disableJavaScriptURLs = false;
+
+// Not ready to break experimental yet.
+// Modern <StrictMode /> behaviour aligns more with what components
+// components will encounter in production, especially when used With <Offscreen />.
+// TODO: clean up legacy <StrictMode /> once tests pass WWW.
+export const useModernStrictMode = false;
+
+// Not ready to break experimental yet.
+// Remove IE and MsApp specific workarounds for innerHTML
+export const disableIEWorkarounds = __NEXT_MAJOR__;
+
+// Changes the behavior for rendering custom elements in both server rendering
+// and client rendering, mostly to allow JSX attributes to apply to the custom
+// element's object properties instead of only HTML attributes.
+// https://github.com/facebook/react/issues/11347
+export const enableCustomElementPropertySupport = __NEXT_MAJOR__;
+
+// Filter certain DOM attributes (e.g. src, href) if their values are empty
+// strings. This prevents e.g. <img src=""> from making an unnecessary HTTP
+// request for certain browsers.
+export const enableFilterEmptyStringAttributesDOM = __NEXT_MAJOR__;
+
 // -----------------------------------------------------------------------------
 // Chopping Block
 //
@@ -145,8 +180,6 @@ export const createRootStrictEffectsByDefault = false;
 
 export const disableModulePatternComponents = false;
 
-export const disableLegacyContext = false;
-
 export const enableUseRefAccessWarning = false;
 
 // Enables time slicing for updates that aren't wrapped in startTransition.
@@ -168,29 +201,12 @@ export const allowConcurrentByDefault = false;
 // in open source, but www codebase still relies on it. Need to remove.
 export const disableCommentsAsDOMContainers = true;
 
-// Disable javascript: URL strings in href for XSS protection.
-export const disableJavaScriptURLs = false;
-
 export const enableTrustedTypesIntegration = false;
 
 // Prevent the value and checked attributes from syncing with their related
 // DOM properties
 export const disableInputAttributeSyncing = false;
 
-// Remove IE and MsApp specific workarounds for innerHTML
-export const disableIEWorkarounds = __EXPERIMENTAL__;
-
-// Filter certain DOM attributes (e.g. src, href) if their values are empty
-// strings. This prevents e.g. <img src=""> from making an unnecessary HTTP
-// request for certain browsers.
-export const enableFilterEmptyStringAttributesDOM = __EXPERIMENTAL__;
-
-// Changes the behavior for rendering custom elements in both server rendering
-// and client rendering, mostly to allow JSX attributes to apply to the custom
-// element's object properties instead of only HTML attributes.
-// https://github.com/facebook/react/issues/11347
-export const enableCustomElementPropertySupport = __EXPERIMENTAL__;
-
 // Disables children for <textarea> elements
 export const disableTextareaChildren = false;
 
@@ -240,8 +256,4 @@ export const enableProfilerNestedUpdateScheduledHook = false;
 
 export const consoleManagedByDevToolsDuringStrictMode = true;
 
-// Modern <StrictMode /> behaviour aligns more with what components
-// components will encounter in production, especially when used With <Offscreen />.
-// TODO: clean up legacy <StrictMode /> once tests pass WWW.
-export const useModernStrictMode = false;
 export const enableDO_NOT_USE_disableStrictPassiveEffect = false;