Introduce support for plugin-defined intrinsics in old JVM backend:

(Old is created first because all intrinsics emit bytecode anyway)

Provide intrinsic for serializer<T>() function so it won't
invoke typeOf() construction and KType->KSerializer conversion
making it fast and truly reflectionless

Add support for recalculating stack size in plugin-defined intrinsics
since it is needed for correct work:
Unify method for recalculating stack size with existing typeOf intrinsic

Add testdata for IR for future intrinsic in IR

plugins/kotlinx-serialization/testData/codegen/Intrinsics.kt

@@ -0,0 +1,43 @@
+// CURIOUS_ABOUT test
+// WITH_STDLIB
+
+import kotlinx.serialization.*
+
+@Serializable
+class Simple(val firstName: String, val lastName: String)
+
+@Serializable
+data class Box<out T>(val boxed: T)
+
+@Serializable
+object SerializableObject {}
+
+inline fun <reified T: Any> getSer(): KSerializer<T> {
+    return serializer<T>()
+}
+
+inline fun <reified T: Any> getBoxSer(): KSerializer<Box<T>> {
+    return serializer<Box<T>>()
+}
+
+inline fun <reified T: Any> listSer(): KSerializer<List<T>> {
+    return serializer<List<T>>()
+}
+
+fun test() {
+    serializer<Simple>()
+    getSer<Simple>()
+    getSer<Box<Simple>>()
+    getBoxSer<Simple>()
+    listSer<Simple>()
+
+    serializer<Box<List<Simple>>>()
+
+    listSer<Box<List<Simple>>>()
+
+    serializer<Int>()
+
+    serializer<SerializableObject>()
+
+    listSer<List<Box<Int>>>()
+}