Add Android-changed markers to String.java.

This change adds markers for all changes relative to OpenJDK 8u121-b13
(although the more mechanical changes are covered by a catch-all
rather than line-by-line). It also reverts a couple of trivial
differences compared to upstream which were seemingly missed (e.g. a
period in some javadoc) and removes some unused imports.

Test: make checkbuild
Change-Id: Ia8b9e5b1534fe1bc0c38abce2b5badaffde3c67f
1 file changed