[tests] Refactor AbstractReferenceResolveTest. Part 1

Instead of relying on UNRESOLVED_REFERENCE directive for the whole file,
just render the unresolved reference right in the .txt testdata

This will allow to introduce multi-caret resolve testdata more naturally

Required for KT-65152 and KT-62695

analysis/analysis-api/testData/referenceResolve/withErrors/FakeJavaLang2.kt

@@ -1,4 +1,3 @@
-// UNRESOLVED_REFERENCE
 // FILE: main.kt
 fun foo() {
     <caret>Fake() // not imported within "java.lang.*" default import