JVM: change logic of applying KT-57570 behavior a bit

If `-Xno-unified-null-checks` is specified, do not throw exceptions, but
rather revert to the old behavior, with source code in exception
messages.

Note that `-Xno-unified-null-checks` is a flag which enables behavior of
Kotlin 1.3. It can be removed once we no longer support API version 1.3.

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

@@ -764,7 +764,7 @@ private class TypeOperatorLowering(private val backendContext: JvmBackendContext
     }
 
     private fun IrBuilderWithScope.computeNotNullAssertionText(typeOperatorCall: IrTypeOperatorCall): String? {
-        if (backendContext.state.languageVersionSettings.supportsFeature(LanguageFeature.NoSourceCodeInNotNullAssertionExceptions)) {
+        if (backendContext.state.noSourceCodeInNotNullAssertionExceptions) {
             return when (val argument = typeOperatorCall.argument) {
                 is IrCall -> "${argument.symbol.owner.name.asString()}(...)"
                 is IrGetField -> argument.symbol.owner.name.asString()