RFR: 8184021: Fix tables in jaxp doc comments to be accessible

[Jonathan Gibbons]

Please review the following fixes to the doc comments in the jaxp repo.

The primary goal is to fix user-written tables in doc comments for 
accessibility, either by updating tables to use scope=row|col in header 
cells for simple tables, or by using the headings attribute in more 
complex tables.  The majority of the changes, to tables using 
class="striped", were done mechanically, using a custom Java utility. 
Three tables were fixed up manually.

In addition, I removed the use of <p> tags which introduced empty 
paragraph. These tags caused warnings when checking the code with the 
"tidy" program.

JBS: https://bugs.openjdk.java.net/browse/JDK-8184021
Webrev: http://cr.openjdk.java.net/~jjg/8184021/webrev.00/

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The following list of comments about the changes is ordered according to 
the list in the webrev.

Catalog:
     removed empty <p>

CatalogFeatures:
     first table updated manually (class="plain")
     removed empty <p>
     second table updated with utility

CatalogResolver:
     removed empty <p>

DatatypeFactory, Duration:
    table updated with utility

XMLGregorianCalendar:
    all tables updated with utility

datatype/package-info:
    table updated with utility

NamespaceContext:
    all tables updated with utility

XMLEventWriter, XMLInputFactory, XMLOutputFactory, XMLStreamReader:
    table updated with utility

XMLStreamWriter:
     this is the one table with class="striped" that had to be updated
     manually, because of the complex headers

SchemaFactory:
     table updated with utility, but table organization could be 
improved (by spec owner)
     for example, to split first column into a name and a URI, and/or 
use the second
     column as a row header.

Validator, XPath, XPathExpression, xpath/package-info:
    table updated manually (class="plain")

Attr
    table updated with utility
    table could be improved by removing redundant atributes, like 
rowspan='1' colspan='1'

Document, Node:
    all tables updated with utility

-- Jon