[JVM] Validate lowered JVM IR only if it was explicitly requested

This is an addition to the f5bb477459
commit. Earlier, some of the validation checks were moved from
`stickyPostconditions` into separate lowering. But these
post-conditions checks were launched only when several flags were
set to true. In this commit, we just return to such behavior.

#KT-64116

compiler/ir/backend.jvm/lower/src/org/jetbrains/kotlin/backend/jvm/JvmLoweringPhases.kt

@@ -82,7 +82,7 @@ private val validateIrAfterLowering = makeCustomPhase(
 )
 
 private val validateJvmIrAfterLowering = makeCustomPhase<JvmBackendContext>(
-    { _, module -> validateJvmIr(module) },
+    { context, module -> validateJvmIr(context, module) },
     name = "ValidateJvmIrAfterLowering",
     description = "Validate that IR after lowering is correctly structured by Kotlin JVM rules"
 )

compiler/ir/backend.jvm/lower/src/org/jetbrains/kotlin/backend/jvm/lower/irValidation.kt

@@ -27,7 +27,9 @@ private fun checkAllFileLevelDeclarationsAreClasses(module: IrModuleFragment) {
     })
 }
 
-fun validateJvmIr(module: IrModuleFragment) {
+fun validateJvmIr(context: JvmBackendContext, module: IrModuleFragment) {
+    if (!context.config.shouldValidateIr) return
+
     checkAllFileLevelDeclarationsAreClasses(module)
     val validator = object : IrElementVisitorVoid {
         override fun visitElement(element: IrElement) {