This is a repeat of JDK-8215307, which is to fix the headings in generated pages to start at <h1>.  The previous fix failed because of a bug in the test and a dependence on the order of iterating the contents of a directory on some systems. The previous fix was backed out with JDK-8219558.

After fixing the test to behave consistently on all platforms, two additional issues were identified, which caused the tests to fail on some platforms. The single- and split- index pages still had no <h1>, and neither did the index file written by AbstractPackageIndexWriter in some cases.

The fix for the single- and split- index pages was to just add the heading, although that did require minor local restructuring of the code.  The fix for AbstractPackageIndexWriter was to copy the equivalent code already written for AbstractModuleIndexWriter.

The fix for the test was simply to reset the current heading "level" when beginning to read each new file. (Previously, it was not reset when beginning to read the file, and so was left at the last value seen in the previous file.) The term is now renamed to "rank" in accordance with W3C terminology