Refactor fullscreen rejection handling to use WebIDL react pattern

This commit modernizes how the Screen Orientation specification responds to
fullscreen request rejections by using the WebIDL 'react' concept instead
of the previous flag-based approach.

Changes:
- Replace flag-based 'pending fullscreen request flag unset due to rejection' pattern
- Use WebIDL 'react' pattern with 'pending fullscreen request promise'
- Update reference to use proper 'pending fullscreen request flag' terminology
- Extract duplicated descendant document logic into helper algorithm 'reject descendant document orientation promises'
- Add clarifying notes for algorithm logic and same-origin security restrictions
- Maintain all existing algorithm behavior while modernizing the specification architecture

This enables cleaner, more maintainable specification text that follows modern
WebIDL patterns for promise-based APIs and eliminates code duplication. The change
complements the fullscreen spec changes in whatwg/fullscreen that add both the
exported flag and promise definitions needed for this integration.

Fixes #254
Fixes #255

Author: marcoscaceres

index.html

@@ -859,19 +859,76 @@ <h2>
         <li>[=Apply orientation lock=] `null` to |topDocument|.
         </li>
       </ol>
+      <h2>
+        Rejecting descendant document orientation promises
+      </h2>
+      <p>
+        To <dfn>reject descendant document orientation promises</dfn> for a {{Document}} |document|, the [=user agent=] MUST:
+      </p>
+      <ol class="algorithm">
+        <li>If |document| is not a [=top-level browsing context=]'s [=navigable/active document=], abort these steps.
+        
+        <p class="note">Only top-level documents have descendant navigables to process.</p></li>
+        <li>Let |descendantDocs| be an [=ordered set=] consisting of |document|'s
+        [=Document/descendant navigables=]'s [=navigable/active documents=], if any, in tree order.</li>
+        <li>[=Set/For each=] |descendantDoc:Document| in |descendantDocs|:
+          <ol>
+            <li>If |descendantDoc| is not [=same origin=] with |document|, continue.
+            
+            <p class="note">Only same-origin descendant documents are processed to prevent cross-origin documents from detecting orientation lock states of their embedding documents, which could be used for timing attacks or fingerprinting.</p></li>
+            <li>If |descendantDoc|'s {{Document/[[orientationPendingPromise]]}} is not `null`,
+            [=reject and nullify the current lock promise=] of |descendantDoc| with an {{"AbortError"}}.</li>
+          </ol>
+        </li>
+      </ol>
     </section>
     <section id="fullscreen-interaction">
       <h2>
         Interaction with Fullscreen API
       </h2>
       <p>
         A user agent SHOULD restrict the use of {{ScreenOrientation/lock()}} to
-        simple fullscreen documents as a [=pre-lock condition=]. [[fullscreen]]
+        documents that meet the <dfn>fullscreen pre-lock condition</dfn> as a
+        [=pre-lock condition=]. [[fullscreen]]
+      </p>
+      <p>
+        A {{Document}} |document| meets the [=fullscreen pre-lock condition=]
+        if any of the following are true:
+      </p>
+      <ol>
+        <li>|document| has a [=fullscreen element=].
+        </li>
+        <li>|document| has its [=pending fullscreen request flag=] set.
+        </li>
+        <li>|document| is [=same origin=] with its [=top-level browsing
+        context=]'s [=navigable/active document=], and that [=top-level
+        browsing context=]'s [=navigable/active document=] meets one of the
+        above conditions.
+        </li>
+      </ol>
+      <p class="note">
+        The third condition allows same-origin iframes to lock the screen
+        orientation when their parent document is in fullscreen or has
+        requested fullscreen. This prevents cross-origin documents from
+        detecting the fullscreen state of their embedding document.
+      </p>
+      <p>
+        When a [=document=] |doc| exits fullscreen, the user agent MUST:
       </p>
+      <ol class="algorithm">
+        <li>Run the [=fully unlock the screen orientation steps=] with |doc|.</li>
+        <li>[=Reject descendant document orientation promises=] for |doc|.</li>
+      </ol>
       <p>
-        When a [=document=] exits fullscreen, it also runs the [=fully unlock
-        the screen orientation steps=]. [[fullscreen]]
+        [=React=] to a [=document=] |doc|'s [=pending fullscreen request
+        promise=]. When the promise is [=reject|rejected=], run the following
+        steps:
       </p>
+      <ol class="algorithm">
+        <li>If |doc|'s {{Document/[[orientationPendingPromise]]}} is not `null`,
+        [=reject and nullify the current lock promise=] of |doc| with an {{"AbortError"}}.</li>
+        <li>[=Reject descendant document orientation promises=] for |doc|.</li>
+      </ol>
     </section>
     <section id="appmanifest-interaction">
       <h2>