Backport Improve the implementation of Long.to{Binary,Hex,Octal}String.

It does not use Formatter anymore, and does not require to drop
the leading 0's after the fact.

(cherry picked from commit 9e43ed89ea3c33e4ecdb9753879b25605a42ebd3)

Conflicts:

	javalanglib/src/main/scala/java/lang/Long.scala