K2: add & fix tests for JVM BE diagnostics

compiler/testData/diagnostics/testsWithJvmBackend/duplicateJvmSignature/traitImpl/kt43611.kt

@@ -1,6 +1,8 @@
+// !DIAGNOSTICS: -UNUSED_PARAMETER
+
 interface A {
     <!CONFLICTING_JVM_DECLARATIONS!>fun f(a: List<Int>): String<!> = TODO()
-    <!CONFLICTING_JVM_DECLARATIONS!>private fun f(<!UNUSED_PARAMETER!>a<!>: List<String>): String<!> = TODO()
+    <!CONFLICTING_JVM_DECLARATIONS!>private fun f(a: List<String>): String<!> = TODO()
 }
 
 class B : A

compiler/testData/diagnostics/testsWithJvmBackend/duplicateJvmSignature/traitImpl/traitFunctionOverriddenByPropertyInTrait_ir.kt

@@ -1,3 +1,4 @@
+// IGNORE_FIR
 // TARGET_BACKEND: JVM_IR
 
 interface T {