JVM_IR KT-49136 don't optimize null checks on fields and calls

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/CommonBackendContext.kt

@@ -64,4 +64,7 @@ interface CommonBackendContext : BackendContext, LoggingContext {
 
     val optimizeLoopsOverUnsignedArrays: Boolean
         get() = false
+
+    val optimizeNullChecksUsingKotlinNullability: Boolean
+        get() = true
 }

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/IfNullExpressionsFusionLowering.kt

@@ -146,9 +146,9 @@ class IfNullExpressionsFusionLowering(val context: CommonBackendContext) : FileL
                 is IrGetClass ->
                     false
                 is IrCall ->
-                    if (!type.isNullable()) false else null
+                    if (context.optimizeNullChecksUsingKotlinNullability && !type.isNullable()) false else null
                 is IrGetField ->
-                    if (!type.isNullable()) false else null
+                    if (context.optimizeNullChecksUsingKotlinNullability && !type.isNullable()) false else null
                 is IrBlock -> {
                     val singleExpr = statements.singleOrNull()
                     if (singleExpr is IrExpression && singleExpr.type == type)