Notify compilation provider on file deletion

[evacchi]

Description
Currently compilation provider is only invoked when a file is added or updated, it may be usefl to receive a notification when a file is removed

Implementation ideas
a separate method with a set of deleted files, or a Set(Deleted(file), Updated(file))

e.g. in Kogito we need to know whether a source file (process, rule) has been removed, to update the indexes we use at runtime, and possibly remove class file that may have been already generated

we can further discuss this and provide a PR

[gsmet]

@machi1990 would you be interested in working on this?

[evacchi]

sure, I'll see if I can spare some cycles

[geoand]

Is this still needed?

[evacchi]

on our side (Kogito), that would be helpful -- assuming we keep using the CompilationProvider mechanism. This should trigger a big with any CompilationProvider; e.g.

1. create Foo.java, reload
2. Foo.class is available
3. delete Foo.java, reload
4. Foo.class is still loaded (?) -- unless the compilation provider knows that Foo.java has been deleted -- so that it can delete the corresponding Foo.class (*)

spoiler alert: because of such complications, I myself am considering if it's worth using the CompilationProvider mechanism or just revert to "plain" extension-based reload (which would trigger a full rebuild instead of a patch)

(*) strong assumptions are being made here on the contents of the files: e.g. Foo.java may contain non-public class Bar