Refactor plugin registration and add ABI/license check

Remove the boilerplate and multiple symbols required
to write and load a plugin and use a simpler
interface that is also much more featureful and
extensible.

This removes the major.minor ABI check in favor of an
ABI version number that is simpler and more flexible.

In practice our 3 separate ABI versions still increase
with each major.minor version number but this may change
in the future, particularly for codecs that have a much
narrower and stable codec API.

There is a new license compatibility check. Plugins
must declare if the use GPLv2 or later, or alternatively
an FSF compliant GPLv2 compatible license. Otherwise
Wireshark refuses to load the plugin. The SPDX ID is
just an ancillary field and not enforced currently.

Adds more metadata fields during plugin registration.
These are only used for display and debugging.

There is an extra API level number in the registration API
that is reserved for future use.