This commit adds the infrastructure to plugin building and loading to
allow one plugin to extend another. That is, one plugin may extend
another by the "parent" plugin allowing itself to be extended through
java SPI. When all plugins extending a plugin are finished loading, the
"parent" plugin has a callback (through the ExtensiblePlugin interface)
allowing it to reload SPI.
This commit also adds an example plugin which uses as-yet implemented
extensibility (adding to the painless whitelist).
* Splits nio project into two for eclipse build only
https://github.com/elastic/elasticsearch/pull/27801 introduced a new gradle project `:libs:elasticsearch-nio` which creates cyclical project dependencies when importingthe projects into Eclipse.
This change applies the same trick as we have for the core project where, and building for Eclipse, splits the `:libs:elasticsearch-nio` project into `:libs:elasticsearch-nio` which points to `src/main` and `:libs:elasticsearch-nio-tests` which points to `src/test`. This prevents cyclical project dependencies in Eclipse arising from the fact that eclipse does not separate compile/runtime dependencies from test dependencies.
* Removes integTest bits since there are none
This is related to #27802. This commit adds a jar called
elasticsearch-nio that contains the base nio classes that will be used
for the tcp nio transport and eventually the http nio transport.
The jar does not depend on elasticsearch:core, so all references to core
have been removed.
Ryan Ernst
Colin Goodheart-Smithe
Tim Brooks