[klib tool] Return unbound symbols for dump-ir mode

This is more convenient behaviour for debugging with klib-tool than
just failing.

Note that enabling Partial Linkage globally in klib-tool is undesirable,
as it can auto-tweak IR (e.g. when overrides do not match), thus
distorting the rendered IR

^KT-61143 Fixed

kotlin-native/klib/src/main/kotlin/org/jetbrains/kotlin/cli/klib/main.kt

@@ -274,6 +274,10 @@ class Library(val libraryNameOrPath: String, val requestedRepository: String?) {
             friendModules = emptyMap(),
             partialLinkageSupport = PartialLinkageSupportForLinker.DISABLED,
         )
+
+        override val returnUnboundSymbolsIfSignatureNotFound: Boolean
+            get() = true
+
         override val translationPluginContext: TranslationPluginContext
             get() = TODO("Not needed for ir dumping")