K2: report JVM backend errors in the same way in PSI as LT

Do not try to find PSI element, but always use the IR element offsets
instead. This greatly simplifies test data because we don't need to have
custom PSI- and LT- based diagnostic ranges in every test, and K1/K2
behavior also is mostly the same.

The exact offset ranges are not as important for backend diagnostics, so
it's better to have K2+PSI and K2+LT behaving the same.

compiler/ir/backend.jvm/codegen/src/org/jetbrains/kotlin/backend/jvm/codegen/JvmSignatureClashDetector.kt

@@ -6,6 +6,7 @@
 package org.jetbrains.kotlin.backend.jvm.codegen
 
 import org.jetbrains.kotlin.backend.common.lower.ANNOTATION_IMPLEMENTATION
+import org.jetbrains.kotlin.backend.common.sourceElement
 import org.jetbrains.kotlin.backend.jvm.JvmLoweredDeclarationOrigin
 import org.jetbrains.kotlin.descriptors.DescriptorVisibilities
 import org.jetbrains.kotlin.diagnostics.KtDiagnosticFactory1
@@ -145,8 +146,10 @@ class JvmSignatureClashDetector(
         irDeclarations: Collection<IrDeclaration>,
         conflictingJvmDeclarationsData: ConflictingJvmDeclarationsData
     ) {
-        irDeclarations.mapNotNullTo(LinkedHashSet()) { irDeclaration ->
-            classCodegen.context.ktDiagnosticReporter.atFirstValidFrom(irDeclaration, classCodegen.irClass, containingIrFile = irDeclaration.file)
+        irDeclarations.mapTo(LinkedHashSet()) { irDeclaration ->
+            // Offset can be negative (SYNTHETIC_OFFSET) for delegated members; report an error on the class in that case.
+            val reportOn = irDeclaration.takeUnless { it.startOffset < 0 } ?: classCodegen.irClass
+            classCodegen.context.ktDiagnosticReporter.at(reportOn.sourceElement(), reportOn, irDeclaration.file)
         }.forEach {
             it.report(diagnosticFactory1, conflictingJvmDeclarationsData)
         }