Add codegeneration of methods with covariant return types

Contents of README.google:
Name: libcore
URL: https://source.android.com/
Version: Libcore AOSP master 0685278b97dd2592e3419f317a773da6c697272e
Revision: NA
License: The GNU General Public License (GPL)

Description:
This is the core-oj.jar pulled from building aosp master.

Bug: b/234579501
Bug: b/232891189
Change-Id: I63b240bb3d589af73efd14a1b0d1aea754a8870d
diff --git a/.gitignore b/.gitignore
index b19c671..bd447f4 100644
--- a/.gitignore
+++ b/.gitignore
@@ -41,6 +41,8 @@
 third_party/android_jar/lib-v[0-9][0-9]
 third_party/android_jar/lib-v[0-9][0-9].tar.gz
 third_party/android_jar/lib.tar.gz
+third_party/android_jar/libcore_latest
+third_party/android_jar/libcore_latest.tar.gz
 third_party/android_jar/api-versions.tar.gz
 third_party/android_jar/api-versions
 third_party/android_sdk