[Rev 03] RFR: Add out-of-the-box support for IntelliJ IDEA

[Erik Helin]

> Hi all,
> 
> please review this PR that adds "out of the box" support for IntelliJ IDEA for
> Skara. The changes primarily consists of:
> 
> - IntelliJ IDEA configuration files
> - Re-working the build system to support one JRE for running Gradle and one JDK
>   for building and testing Skara
> - Documentation updates
> 
> The build changes are a bit messy, I will refactor them later, but I want to
> await feedback first to see if we need to some additional changes.
> 
> Testing:
> - Opening up the Skara root directory in a fresh install of IntelliJ IDEA on
>   Linux x64
> 
> Thanks,
> Erik

Erik Helin has updated the pull request with a new target base due to a merge or a rebase. The pull request now
contains four commits:

 - Merge master
 - Fix Windows build
 - Fix macOS build
 - Add out-of-the-box support for IntelliJ IDEA

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Changes: https://git.openjdk.java.net/skara/pull/489/files
 Webrev: https://webrevs.openjdk.java.net/skara/489/webrev.03
  Stats: 377 lines in 14 files changed: 363 ins; 3 del; 11 mod
  Patch: https://git.openjdk.java.net/skara/pull/489.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/489/head:pull/489

PR: https://git.openjdk.java.net/skara/pull/489