eca_render.action_base is inherited by plugins that never set its keys

Noticed while working #3590380 (closed).

The eight action.configuration.eca_render_alter_link_* sections, plus eca_render_serialize and eca_render_unserialize, declare type: eca_render.action_base and therefore inherit weight, name, token_name and mode. None of those plugins ever set those keys — their defaultConfiguration() does not define them, and they show as absent at runtime.

So the schema documents keys these plugins do not have. #3590380 (closed) makes this more visible, since those sections now also carry the retyped eca_integer_or_token keys they never use.

This is pre-existing, introduced with the new sections in #3590379 (closed), and was deliberately kept out of #3590380 (closed) to keep that fix reviewable.

Resolution is probably to split eca_render.action_base into a minimal base plus a render-element base carrying the element-specific keys, and repoint the families that do not need them.

Change record: #3616767