fix: Read identityMode from first skeleton that defines it

When multiple targets share one createInstantiator (e.g. test package),
use compactMap to find the first non-nil identityMode across all skeletons
instead of reading from the first skeleton which may not have it set.

Author: krodak

Plugins/BridgeJS/Sources/BridgeJSLink/BridgeJSLink.swift

@@ -983,7 +983,7 @@ public struct BridgeJSLink {
 
         try printer.indent {
             printer.write(lines: generateVariableDeclarations())
-            let configIdentityMode = skeletons.compactMap(\.exported).first?.identityMode ?? "none"
+            let configIdentityMode = skeletons.compactMap(\.exported).compactMap(\.identityMode).first ?? "none"
             printer.write("const identityMode = options.identityMode ?? \"\(configIdentityMode)\";")
             printer.write(
                 "const shouldUseIdentityMap = identityMode === \"pointer\" && typeof WeakRef !== \"undefined\" && typeof FinalizationRegistry !== \"undefined\";"