IR: minor, give names to anonymous lowering visitors

To improve stacktraces and make the code a bit more readable.

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/Lower.kt

@@ -76,29 +76,37 @@ fun FileLoweringPass.lower(moduleFragment: IrModuleFragment) = moduleFragment.fi
 //}
 
 fun ClassLoweringPass.runOnFilePostfix(irFile: IrFile) {
-    irFile.acceptVoid(object : IrElementVisitorVoid {
+    irFile.acceptVoid(ClassLoweringVisitor(this))
+}
+
+private class ClassLoweringVisitor(
+    private val loweringPass: ClassLoweringPass
+) : IrElementVisitorVoid {
     override fun visitElement(element: IrElement) {
         element.acceptChildrenVoid(this)
     }
 
     override fun visitClass(declaration: IrClass) {
         declaration.acceptChildrenVoid(this)
-            lower(declaration)
+        loweringPass.lower(declaration)
     }
-    })
 }
 
 fun ScriptLoweringPass.runOnFilePostfix(irFile: IrFile) {
-    irFile.acceptVoid(object : IrElementVisitorVoid {
+    irFile.acceptVoid(ScriptLoweringVisitor(this))
+}
+
+private class ScriptLoweringVisitor(
+    private val loweringPass: ScriptLoweringPass
+) : IrElementVisitorVoid {
     override fun visitElement(element: IrElement) {
         element.acceptChildrenVoid(this)
     }
 
     override fun visitScript(declaration: IrScript) {
         declaration.acceptChildrenVoid(this)
-            lower(declaration)
+        loweringPass.lower(declaration)
     }
-    })
 }
 
 fun DeclarationContainerLoweringPass.asClassLoweringPass() = object : ClassLoweringPass {
@@ -125,8 +133,17 @@ fun BodyLoweringPass.runOnFilePostfix(
     withLocalDeclarations: Boolean = false,
     allowDeclarationModification: Boolean = false
 ) {
-    ArrayList(irFile.declarations).forEach {
+    val visitor = BodyLoweringVisitor(this, withLocalDeclarations, allowDeclarationModification)
-        it.accept(object : IrElementVisitor<Unit, IrDeclaration?> {
+    for (declaration in ArrayList(irFile.declarations)) {
+        declaration.accept(visitor, null)
+    }
+}
+
+private class BodyLoweringVisitor(
+    private val loweringPass: BodyLoweringPass,
+    private val withLocalDeclarations: Boolean,
+    private val allowDeclarationModification: Boolean,
+) : IrElementVisitor<Unit, IrDeclaration?> {
     override fun visitElement(element: IrElement, data: IrDeclaration?) {
         element.acceptChildren(this, data)
     }
@@ -144,10 +161,10 @@ fun BodyLoweringPass.runOnFilePostfix(
     override fun visitBody(body: IrBody, data: IrDeclaration?) {
         if (withLocalDeclarations) body.acceptChildren(this, null)
         if (allowDeclarationModification) {
-                    lower(body, data!!)
+            loweringPass.lower(body, data!!)
         } else {
             stageController.bodyLowering {
-                        lower(body, data!!)
+                loweringPass.lower(body, data!!)
             }
         }
     }
@@ -159,9 +176,6 @@ fun BodyLoweringPass.runOnFilePostfix(
         }
         declaration.thisReceiver.accept(this, declaration)
     }
-
-        }, null)
-    }
 }
 
 fun FunctionLoweringPass.runOnFilePostfix(irFile: IrFile) {