RFR: JDK-8267204: Expose access to underlying streams in DocletEnvironment

[Pavel Rappo]

On Tue, 18 May 2021 00:38:40 GMT, Jonathan Gibbons <jjg at openjdk.org> wrote:

> Please review a relatively simple update to expose the 1 or 2 streams available within javadoc for writing expected or diagnostic output.
> 
> The change at this time is just to _expose_ the streams; followup work may change how we _use_ them.
> 
> There are two points of note:
> 
> * `JavadocTester` is extended to provided access to the javadoc entry point used by the launcher. This is simpler than exec-ing the tool to invoke the entry point, and allows us to use the existing code to capture and analyze the output.
> * The initialization of the default streams in `Messager` is deferred, to allow `Messager` to use the values of `System.out` and `System.err` at the time that javadoc is started, instead of when the class was loaded. This is part of the problems described separately in JDK-8267203, but which needs to be addressed here as part of this work.

This PR has been superseded by https://github.com/openjdk/jdk/pull/4216.

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PR: https://git.openjdk.java.net/jdk/pull/4077