REGRESSION (278562@main): IPCTestingAPI.SerializedTypeInfo is a consi…

…stent failure

https://bugs.webkit.org/show_bug.cgi?id=274133
rdar://128026967

Reviewed by Aditya Keerthi, Abrar Rahman Protyasha and Tim Horton.

Add `using WebCore::TargetedElementSelectors = …;` to the IPC serialization file, so that the
generated IPC testing code treats `TargetedElementSelectors` as a type alias instead of a separate
type that requires its own serializer.

Currently, this causes the API test `IPCTestingAPI.SerializedTypeInfo` to fail.

* Source/WebKit/Shared/WebCoreArgumentCoders.serialization.in:

Drive-by refactoring: also add an alias for `TargetedElementIdentifiers`, and use it below for
consistency (and readability).

Canonical link: https://commits.webkit.org/278731@main

Source/WebKit/Shared/WebCoreArgumentCoders.serialization.in

@@ -887,10 +887,13 @@ struct WebCore::ShareData {
 
 enum class WebCore::ShareDataOriginator : bool
 
+using WebCore::TargetedElementIdentifiers = std::pair<WebCore::ElementIdentifier, WebCore::ScriptExecutionContextIdentifier>;
+using WebCore::TargetedElementSelectors = Vector<HashSet<String>>;
+
 header: <WebCore/ElementTargetingTypes.h>
 [CustomHeader] struct WebCore::TargetedElementAdjustment {
-    std::pair<WebCore::ElementIdentifier, WebCore::ScriptExecutionContextIdentifier> identifiers
-    Vector<HashSet<String>> selectors
+    WebCore::TargetedElementIdentifiers identifiers
+    WebCore::TargetedElementSelectors selectors
 };
 
 header: <WebCore/ElementTargetingTypes.h>