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

Add intrinsic for kotlinx.serialization.serializer<T>() function.

Plugin intrinsic for old backend is removed because it is too hard
and unjustifiable to unify them.

plugins/kotlinx-serialization/kotlinx-serialization.backend/build.gradle.kts

@@ -9,6 +9,7 @@ dependencies {
     compileOnly(project(":compiler:backend"))
     compileOnly(project(":compiler:ir.backend.common"))
     compileOnly(project(":compiler:backend.jvm"))
+    compileOnly(project(":compiler:backend.jvm.codegen"))
     compileOnly(project(":compiler:ir.tree"))
     compileOnly(project(":js:js.frontend"))
     compileOnly(project(":js:js.translator"))