RFR: 8187521: In some corner cases the javadoc tool can reuse id attribute

[Jonathan Gibbons]

Please review this fix regarding the handling of ID values generated by 
the standard javadoc doclet.

The root cause of the specific issue is a corner case in Java. A class 
may contain a method
with the same name as the enclosing class, and any corresponding 
constructor.

The fix is to use a different name for the name of the constructor that 
cannot clash with
any method name, with `<init>` being the obvious choice.

The fix is restricted, along with some other changes, to when generating 
HTML5 docs.
There are other problems with IDs/anchor names when using HTML 4.01, 
which are all
better addressed by using HTML5, leaving support for HTML 4.01 unchanged 
at this point.

In HTML5, there are no restrictions on the individual characters in an 
ID other than to prohibit
whitespace. Therefore, there is no longer any need to use the 
javadoc-specific encoding
using `:` and `-` to encode otherwise invalid characters. Thus, the ID 
for a member of the class
is just the signature of the member: the name for a field, the name and 
parameter-type list
for a method, and `<init>` and parameter-type list for a constructor.

Finally, because this opens up the possibility of square brackets 
appearing in a signature
(where previously "[]" was encoded as ":A"), the encoding of URLs which 
have fragments
containing [] had to be improved, by using the standard URL %-encoding 
for these characters.

The tests are updated, with additional tests being added for members 
with non-ASCII
identifiers, to verify that IDs and defined and referenced correctly.

JBS: https://bugs.openjdk.java.net/browse/JDK-8187521
Webrev: http://cr.openjdk.java.net/~jjg/8187521/webrev.00/index.html

-- Jon