[foreign] RFR 8219932: Split jextract's Context into multiple (immutable) sub-components

[Jorn Vernee]

Hi,

Continuing this from an earlier thread [1]. Here is the first iteration 
of the ideas that were discussed.

This patch splits up Context into multiple sub-components. These are:

- Options, a collection of options for a jextract run.
- Log, logging PrintWriters + Logger
- A List<Path> with jextract source (.h) files.

Context is then used as an argument to a particular jextract run.

I've held off on adding JextractTool as a sub-component as well, since 
that would create a circular dependency, and I'm not sure what the 
advantage of adding it would be at this time, since it's not accessed by 
other internal parts of the jextract run.

I've moved some functions to other classes, where I felt they made more 
sense;

- Main.format -> Log.format
- Main.getBuiltinHeadersDir -> Context.getBuiltinHeadersDir
- Context.findLibraryPath -> Utils.findLibraryPath

To support the immutability of the Options sub-component I created a 
builder for it, and moved the code that creates it to a separate method 
in Main. In some cases the code wanted to exit early and return an exit 
code, this is now replaced with throwing a custom exception, which is 
caught in the `int run(String[] args)`  method.

Bug: https://bugs.openjdk.java.net/browse/JDK-8219932
Webrev: 
http://cr.openjdk.java.net/~jvernee/panama/webrevs/8219932/webrev.00/

Thanks,
Jorn

[1] : 
https://mail.openjdk.java.net/pipermail/panama-dev/2019-February/004627.html