Refactor several items

[bgilbert]

Only wrap FFM exceptions if necessary. Exceptions from FFM invocations are generally RuntimeExceptions, so we can throw them as-is. Any others we need to wrap. In the latter case, wrap with an IllegalArgumentException, since that's a better guess at the cause than AssertionError.

Push locking down into OpenSlideFFM. Implement read-write locking for use-after-free checks in a single place in OpenSlideFFM.Ref, which is logically a better place for it and simplifies the higher-level code.

Deprecate the now-unused, but public, zero-argument OpenSlideDisposedException constructor.

Use AutoCloseable wrapper class for OpenSlide error checks. Rather than manually calling checkError() after every set of OpenSlide calls, introduce a wrapper class which holds the OpenSlideRef and can be used as a resource in a try-with-resources block. When exiting the block, its close() method can then run the error check.

Deprecate OpenSlide.dispose(). close() is more idiomatic because of Closeable and has existed since 2010.

[openslide-bot]

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