Implements alias annotation and allow multiple deserialization renames.

test_suite/tests/ui/duplicate-attribute/rename-rename-de.rs

@@ -1,10 +0,0 @@
-use serde_derive::Serialize;
-
-#[derive(Serialize)]
-struct S {
-    #[serde(rename = "x")]
-    #[serde(rename(deserialize = "y"))]
-    x: (),
-}
-
-fn main() {}

test_suite/tests/ui/duplicate-attribute/rename-rename-de.stderr

@@ -1,8 +0,0 @@
-error: duplicate serde attribute `rename`
- --> $DIR/rename-rename-de.rs:6:13
-  |
-6 |     #[serde(rename(deserialize = "y"))]
-  |             ^^^^^^
-
-error: aborting due to previous error
-