FIR2IR: generate synthetic members for data class only if needed

compiler/testData/codegen/box/dataClasses/equals/alreadyDeclared.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 data class A(val x: Int) {
   override fun equals(other: Any?): Boolean = false
 }

compiler/testData/codegen/box/dataClasses/equals/alreadyDeclaredWrongSignature.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 // TARGET_BACKEND: JVM
 
 // WITH_RUNTIME