Adjust enablement criteria for the "Async UIKit Interactions" feature…

… flag

https://bugs.webkit.org/show_bug.cgi?id=266022

Reviewed by Aditya Keerthi.

Adjust this feature flag, such that it's enabled by default only when both the following criteria
are met:

1. `PAL::deviceClassIsSmallScreen()` is true.
2. `UIKit/async_text_input` is enabled.

* Source/WebKit/Shared/ios/WebPreferencesDefaultValuesIOS.mm:
(WebKit::defaultUseAsyncUIKitInteractions):

Canonical link: https://commits.webkit.org/271703@main

Source/WebKit/Shared/ios/WebPreferencesDefaultValuesIOS.mm

@@ -78,10 +78,10 @@ bool defaultMediaSourceEnabled()
 bool defaultUseAsyncUIKitInteractions()
 {
     static bool enabled = false;
-#if HAVE(UI_ASYNC_TEXT_INTERACTION)
+#if PLATFORM(IOS) && HAVE(UI_ASYNC_TEXT_INTERACTION)
     static std::once_flag flag;
     std::call_once(flag, [] {
-        enabled = os_feature_enabled(UIKit, async_text_input);
+        enabled = PAL::deviceClassIsSmallScreen() && os_feature_enabled(UIKit, async_text_input);
     });
 #endif
     return enabled;