[FIR] Report missing UNRESOLVED_IMPORT

#KT-54781 Fixed

compiler/testData/diagnostics/tests/imports/brokenImport.fir.kt

@@ -1,2 +1,14 @@
-import foo.bar.baz
-import Outer.`<no name provided>`.getInner
+// FILE: Klass.kt
+package pkg
+
+private class Klass
+
+// FILE: test.kt
+package pack
+
+import <!UNRESOLVED_IMPORT!>foo<!>.bar.baz
+import <!UNRESOLVED_IMPORT!>Outer<!>.`<no name provided>`.getInner
+import pack.<!UNRESOLVED_IMPORT!>UnresolvedName<!>
+import pkg.Klass
+
+class MainSource