RFR: 8223678: Add Visual Studio Code workspace generation support (for native code)

[Robin Westberg]

Hi all,

Please review this change that adds build system support for generating a Visual Studio Code workspace configured for working with the JDK native code. It configures the default C/C++ IntelliSense Engine to allow code completion/navigation and similar features. It also configures two executable targets (gtestLauncher and java) that can be built and debugged from the IDE.

The main target is "make vscode-project”, additional information can be found in doc/ide.[md|html].

Issue:
https://bugs.openjdk.java.net/browse/JDK-8223678

Webrev:
https://cr.openjdk.java.net/~rwestberg/8223678/webrev.01/

Testing:
Manual testing on Linux, MacOS and Windows

Thanks Erik Joelsson for taking a look at an earlier version of it! 

Best regards,
Robin