[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/arrayAccess/withErrors/SetOperatorInc.kt

@@ -1,4 +1,3 @@
-// UNRESOLVED_REFERENCE
 package test
 
 class B(val n: Int) {

analysis/analysis-api/testData/referenceResolve/arrayAccess/withErrors/SetOperatorInc.txt

@@ -1,2 +1,2 @@
 Resolved to:
-0: (in test.B) operator fun set(i: kotlin.Int, a: test.B)
+Nothing (Unresolved reference)