Bump minimum Java version to 17 and add Java 21 build

Change-Id: Ia063d5de28cd69152286a3dec4a6f614f1549915

WORKSPACE

diff --git a/WORKSPACE b/WORKSPACE
index 3489ca0..c9e9953 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -33,10 +33,10 @@
     path = "modules/java-prettify",
 )
 
-register_toolchains("//tools:error_prone_warnings_toolchain_java11_definition")
-
 register_toolchains("//tools:error_prone_warnings_toolchain_java17_definition")
 
+register_toolchains("//tools:error_prone_warnings_toolchain_java21_definition")
+
 maven_jar(
     name = "error-prone-annotations",
     artifact = "com.google.errorprone:error_prone_annotations:2.22.0",