[FIR] Microoptimizations and clearing

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirImportsChecker.kt

@@ -22,6 +22,7 @@ import org.jetbrains.kotlin.fir.symbols.impl.*
 import org.jetbrains.kotlin.name.ClassId
 import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.types.expressions.OperatorConventions
+import org.jetbrains.kotlin.utils.addToStdlib.filterIsInstanceWithChecker
 
 object FirImportsChecker : FirFileChecker() {
     override fun check(declaration: FirFile, context: CheckerContext, reporter: DiagnosticReporter) {
@@ -97,8 +98,7 @@ object FirImportsChecker : FirFileChecker() {
 
     private fun checkConflictingImports(imports: List<FirImport>, context: CheckerContext, reporter: DiagnosticReporter) {
         val interestingImports = imports
-            .filterIsInstance<FirResolvedImport>()
-            .filter { import ->
+            .filterIsInstanceWithChecker<FirResolvedImport> { import ->
                 !import.isAllUnder &&
                         import.importedName?.identifierOrNullIfSpecial?.isNotEmpty() == true &&
                         import.resolvesToClass(context)