RFR: JDK-8246712 doclint incorrectly reports some HTML elements as empty

[Jonathan Gibbons]

Please review a simple change to ensure that inline tags are taken into 
account when checking if an HTML element is empty.

As well as testing all existing inline tags, the test also tries to 
avoid future instances of this problem, by testing all subtypes of 
InlineTagTree, and ensuring that each have a corresponding test case.

-- Jon

JBS: https://bugs.openjdk.java.net/browse/JDK-8246712
Webrev: http://cr.openjdk.java.net/~jjg/8246712/webrev.00