RFR: 8181825: Add tool and services information to module summary

[Jonathan Gibbons]

Please review minor doc updates to langtools modules to add info
about tools and services.

In addition, a previously missing package-info is provided for
com.sun.tools.javac.

This is the langtools equivalent of JDK-8181639.
https://bugs.openjdk.java.net/browse/JDK-8181639
http://mail.openjdk.java.net/pipermail/core-libs-dev/2017-June/048132.html

JBS: https://bugs.openjdk.java.net/browse/JDK-8181825
Webrev: http://cr.openjdk.java.net/~jjg/8181825/webrev.00

-- Jon