inlineClassUtils: Fix handling of inline classes without constructors

Fixes KT-50992

DeclarationDescriptor.isInlineClass misidentifies inline classes without
constructors. This can happen for the ABI of inline classes with private
constructors.

plugins/jvm-abi-gen/testData/compile/privateValueClassConstructor/app/app.kt

@@ -0,0 +1,7 @@
+package app
+
+import lib.*
+
+fun runAppAndReturnOk(): String {
+    return A.a().b()
+}

plugins/jvm-abi-gen/testData/compile/privateValueClassConstructor/lib/lib.kt

@@ -0,0 +1,7 @@
+package lib
+
+@JvmInline
+value class A private constructor(val value: String) {
+    companion object { fun a() = A("OK") }
+    inline fun b() = value
+}