KTIJ-26423 [AA] Return more info from KtFirImportOptimizer

Deprecate `unusedImports`, since they are supposed to be computed
on the IDE side from now on based on the information from
Analysis API

Currently the `unusedImports` property is not removed completely
so it can still be used by the Kotlin side import optimizer
tests; they should be moved/adapted to the intellij repository
also

analysis/analysis-api-fir/src/org/jetbrains/kotlin/analysis/api/fir/components/KtFirImportOptimizer.kt

@@ -57,7 +57,7 @@ internal class KtFirImportOptimizer(
 
     override fun analyseImports(file: KtFile): KtImportOptimizerResult {
         val existingImports = file.importDirectives
-        if (existingImports.isEmpty()) return KtImportOptimizerResult(emptySet())
+        if (existingImports.isEmpty()) return KtImportOptimizerResult()
 
         val firFile = file.getOrBuildFirFile(firResolveSession).apply { lazyResolveToPhase(FirResolvePhase.BODY_RESOLVE) }
 
@@ -68,9 +68,10 @@ internal class KtFirImportOptimizer(
             .map { it.fqName }
             .toSet()
 
-        val (usedImports, unresolvedNames) = collectReferencedEntities(firFile)
+        val (usedDeclarations, unresolvedNames) = collectReferencedEntities(firFile)
 
-        val referencesEntities = usedImports
+        // TODO remove unused imports computing code completely
+        val referencesEntities = usedDeclarations
             .filterNot { (fqName, referencedByNames) ->
                 val fromCurrentPackage = fqName.parentOrNull() == file.packageFqName
                 val noAliasedImports = referencedByNames.singleOrNull() == fqName.shortName()
@@ -104,7 +105,7 @@ internal class KtFirImportOptimizer(
             }
         }
 
-        return KtImportOptimizerResult(unusedImports)
+        return KtImportOptimizerResult(unusedImports, usedDeclarations, unresolvedNames)
     }
 
     private data class ReferencedEntitiesResult(