Further refine the Java syntax lexer for escaped strings

Summary:
Ref T13210. See PHI886. Previously, D19731 improved some behavior here, but didn't go quite far enough and we still got strings with \" wrong.

Parse backslash followed by anything, or any character except double quote or backslash.

(If this is still somehow wrong I can just copy one of the other lexers which is a little more complicated but gets this right.)

Test Plan:

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13210

Differential Revision: https://secure.phabricator.com/D19763