WIP: Meson build for MMCoreJ

[marktsuchida]

This is a work in progress.

The goal to aim for is a stand-alone mmcorej repository (initially a mirror of MMCoreJ_wrap/) that is analogous to pymmcore, which publishes to the Maven Central repository.

Major things remaining to do:

• Generate a Javadoc jar
• Generate a source jar (possibly outside of Meson using meson dist)
• Possibly generate pom.xml with version from meson.build (probably not while MMCoreJ lives in mmCoreAndDevices)
• Include pom.xml in jar
• Should version also be in the jar menifest?
• Package JNI libraries (for all supported platforms) in the jar, and auto-extract at runtime (N.B. MMCore uses its binary path as a default search location for device adapters; this may need to be disabled if/when the JNI lib is extracted to a temporary directory)

The Javadoc generation requires some thought. We currently use the ancient swig-doc-converter, which I'd like to retire. SWIG 4 can translate Doxygen to Javadoc, but (a) we still require SWIG 2/3 for MMCoreJ (#37) and (b) the doc comments of MMCore will need to be in the headers for that to work (#23 - probably best to do when no major PRs are outstanding on MMCore). Might be best to tackle those issues first.