Add a java module named "org.libreoffice.unoloader" for this jar.

Require this module from org.libreoffice.uno
(libreoffice.jar has unoloader.jar in its classpath,
so add the same dependency to the modules)

Change-Id: I7471d65ac7a0d2c6a11c002027a21f0c441dd1f2
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/94419
Tested-by: Jenkins
Reviewed-by: Christian Lohmaier <lohmaier+LibreOffice@googlemail.com>

Add a java module named "org.libreoffice.uno" for this jar.

This needs to be compiled with Java 9.
But since we want to keep b/c with Java 8,
the rest of the jar has to be compiled with Java 8.

This bumps the *build* requirement to Java 9 while keeping
the *runtime* requirement at Java 8.

The gbuild JavaClassSet class is changed to invoke javac twice,
where the 2nd invocation compiles with --release 9 and a --patch-modules
argument so that it finds the results of the first invocation and also
the javamaker generated files in CustomTargets.

Change-Id: I888f5dbe097cc37136e68db5919939877c981862
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/91105
Tested-by: Jenkins
Reviewed-by: Christian Lohmaier <lohmaier+LibreOffice@googlemail.com>

This moves the classes from juh.jar and ridl.jar to libreoffice.jar

The goal is to have one single jar (and Java module, will be added later)
which developers can include to work with LO.

juh.jar and ridl.jar are kept as basically empty jars with libreoffice.jar
on its classpath to keep backwards compatibility.

This is a continuation of ae855bf48163ff64d94cfc34aff8e37abdb5518d
and a preparation to have Java 9 module support.

Change-Id: Ifbbfb97f60373d14256e62ae3122913bd17d5bbb
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/91930
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

jurt.jar and unoil.jar are kept as effectively empty jars, each with a

  Class-Path: ridl.jar

in their meta-inf/manifest.mf, so that 3rd-party code loading them (with or
without also loading ridl.jar) will still have access to their content.

Conceptually, the UNOIDL entities in unoil.jar (corresponding to module offapi)
are not part of the URE, but are now made available by URE's ridl.jar.  This
should probably not cause problems in practice.

At least for now, we seal exactly those packages in ridl.jar that were
originally sealed in jurt.jar.  Ideally, all of ridl.jar could be sealed now,
but that would be mildly incompatible, as it would prevent 3rd-party code from
introducing additional UNOIDL entities in the relevant namespaces (even if that
is something we do not want 3rd-party code to do anyway).

However, some JunitTest_jurt_* define classes in those sealed packages.  In the
past they got away with that by using gb_JunitTest_use_jar_classset,*,jurt.
Instead they now need to gb_JunitTest_use_jar_classset,*,ridl and drop the
gb_JunitTest_use_jar,*,ridl.  But the former only makes available the classes
that are specified in ridljar/Jar_ridl.mk with gb_Jar_add_sourcefiles, not the
UNOIDL entities specified via gb_Jar_add_packagedirs.  But the tests need the
udkapi UNOIDL entities, so introduce gb_JunitTest_add_classpath to let the tests
get them explicitly.  (Curiously, JunitTest_jurt_uno and JnitTest_jurt_util use
gb_JunitTest_use_jar_classset,*,jurt but don't seem to acutally need it; lets
leave that for a follow-up clean up.)

As a follow-up clean up, relevant files could be moved from jurt/ to ridljar/.

Change-Id: I836f4e7bb47fb41f1306e3f223da90dba988eb9a
Co-authored-by: Stephan Bergmann <sbergman@redhat.com>
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/84946
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

Set up the toolchain to create sources and javadocs artifacts in
addition to JARs created during the build. Use Buck build tool for
that: [1]. This is a fork of Google's build tool Blaze, created by
Xooglers at Facebook. This build tool (like Blaze itself) uses
Python to write build files.

Add needed tools and build files to install LibreOffice API artifacts
to local Maven repository or deploy them to Maven Central.

To build all needed artifacts LibreOffice must be built regularly
with GNU make first. To build the rest of the API (sources and
javadocs):

  $> buck build api

To replace version number with upcoming release version:

  $> solenv/bin/version.py 5.1.0

To install the API to local Maven repository:

  $> buck build api_install

To deploy the API to Maven Central:

  $> buck build api_deploy

Detailed documentation is added to document the prerequisites and
the workflow to upload LibreOffice API to Maven Central.

* [1] https://buckbuild.com

Change-Id: Ibdd552a01110836703bc069abe829b9921491cac
Reviewed-on: https://gerrit.libreoffice.org/20343
Reviewed-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>
Tested-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>