Fix target for annotations/metadata on open suspend functions

Get rid of rewriting of vars in FunctionCodegen::generateMethod,
just extracted generateMethodBody instead

 #KT-19814 Fixed

compiler/testData/codegen/box/reflection/annotations/openSuspendFun.kt

@@ -0,0 +1,28 @@
+// WITH_REFLECT
+// IGNORE_BACKEND: JS, NATIVE
+
+import kotlin.reflect.full.declaredMemberFunctions
+import kotlin.test.assertEquals
+import kotlin.test.assertTrue
+
+annotation class Anno
+
+open class Aaa {
+    @Anno
+    suspend open fun aaa() {}
+}
+
+class Bbb {
+    @Anno
+    suspend fun bbb() {}
+}
+
+fun box(): String {
+    val bbb = Bbb::class.declaredMemberFunctions.first { it.name == "bbb" }.annotations
+    assertEquals(1, bbb.size)
+    assertTrue(bbb.single() is Anno)
+    val aaa = Aaa::class.declaredMemberFunctions.first { it.name == "aaa" }.annotations
+    assertEquals(1, aaa.size)
+    assertTrue(aaa.single() is Anno)
+    return "OK"
+}

compiler/testData/codegen/box/reflection/mapping/openSuspendFun.kt

@@ -0,0 +1,22 @@
+// WITH_REFLECT
+// IGNORE_BACKEND: JS, NATIVE
+
+import kotlin.reflect.full.declaredMemberFunctions
+import kotlin.reflect.jvm.javaMethod
+import kotlin.test.assertEquals
+
+open class Aaa {
+    suspend open fun aaa() {}
+}
+
+class Bbb {
+    suspend fun bbb() {}
+}
+
+fun box(): String {
+    val bbb = Bbb::class.declaredMemberFunctions.first { it.name == "bbb" }.javaMethod
+    assertEquals("bbb", bbb!!.name)
+    val aaa = Aaa::class.declaredMemberFunctions.first { it.name == "aaa" }.javaMethod
+    assertEquals("aaa", aaa!!.name)
+    return "OK"
+}