RFR: JDK-8254627: Cleanup {Abstract, Single, Split}IndexWriter classes

[Jonathan Gibbons]

On Mon, 12 Oct 2020 22:36:51 GMT, Jonathan Gibbons <jjg at openjdk.org> wrote:

> Inspired by other recent work to cleanup index generation, this change is primarily about cleanup for
> `AbstractIndexWriter`, `SingleIndexWriter`, `SplitIndexWriter` to reduce code duplication and to reduce the 3 class to
> just 1 that can handle either single index files or split index files.  As part of this cleanup, some anomalies were
> uncovered in the naming of annotation types, enum constants and records, which have also been addressed.
> The changes involved moving/merging code from `SingleIndexWriter` and `SplitIndexWriter` in to `AbstractIndexWriter`,
> which is now no longer abstract and is thus renamed to just `IndexWriter`. Regrettably, the rename is not properly
> tracked.

Note that the apparently-new file `IndexWriter.java` is just a rename of the apparently-deleted file
`AbstractIndexWriter.java`.

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PR: https://git.openjdk.java.net/jdk/pull/621