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-impl-base/tests/org/jetbrains/kotlin/analysis/api/impl/base/test/cases/components/importOptimizer/AbstractAnalysisApiImportOptimizerTest.kt

@@ -16,6 +16,7 @@ abstract class AbstractAnalysisApiImportOptimizerTest : AbstractAnalysisApiBased
         val mainKtFile = ktFiles.singleOrNull() ?: ktFiles.first { it.name == "main.kt" }
         val unusedImports = analyseForTest(mainKtFile) {
             val results = analyseImports(mainKtFile)
+            @Suppress("DEPRECATION")
             results.unusedImports
         }