RFR: 8231601: Update CONTRIBUTING.md to clarify process for contributing features plus Skara changes [v3]

[Nir Lisker]

On Wed, 16 Sep 2020 12:54:19 GMT, Kevin Rushforth <kcr at openjdk.org> wrote:

>> The "New features / API additions" repeats some things already stated. Is it to make each section independent?
>
> I wanted the "New features / API additions" section to stand on its own. Once thing that might be redundant now is the
> following sentence in the "Contributing code and documentation changes" section:
> "Feature requests, in particular, must be discussed ahead of time and will require significant effort on your part."
> 
> I think that could be removed or incorporated in "New features / API additions".

I think that "Contributing to the OpenJFX codebase" should be renamed to something related to a style guide. Then split
the testing part to its own subsection.

Also, I still find it confusing that "New features / API additions" is not under the code contribution section. There
seems to be 2 main sections: reporting bugs / requesting features - these don't involve code, just talk; then there is
contributing code, which covers the process for setup, submissions of bugs fixes, submission of features/API, style,
and testing (in some order). Wouldn't this be a better flow?

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PR: https://git.openjdk.java.net/jfx/pull/303