[clang-format] Recognize Java logical shift assignment operator

At present, clang-format mangles Java containing logical right shift operators
('>>>=' or '>>>'), splitting them in two, resulting in invalid code:

 public class Minimal {
   public void func(String args) {
     int i = 42;
-    i >>>= 1;
+    i >> >= 1;
     return i;
   }
 }

This adds both forms of logical right shift to the FormatTokenLexer, so
clang-format won't attempt to split them and insert bogus whitespace.

https://reviews.llvm.org/D31652
Patch from Richard Bradfield <bradfier@fstab.me>!

llvm-svn: 299952