FIR IDE: Search for the first non-local declaration in EnclosingDeclarationContext::detect

Local declarations do not have a stable `ClassId`, which is used in
`declarationUtils.collectDesignation`. Local classes will always have
`outerClassId.isLocal = true`, even when it is not true (see
`org.jetbrains.kotlin.fir.builder.Context.currentClassId` for why this
happens)

idea/idea-completion/testData/basic/common/InsideAnonymousClass.kt

@@ -1,3 +1,4 @@
+// FIR_COMPARISON
 class A(private val xxx1: Int, val xxx2: Int) {
     private val xxx3: Int = 0