Issue #3618250: Resolve an alias through what the resources declare

The path processor turned an alias into an API path with a switch over ten bundle machine names of one particular site, each mapped to a literal endpoint. A site whose content types are named anything else got no answer, and two of the branches named endpoints this module does not ship at all - so those aliases were rewritten to routes that do not exist.

The question "which endpoint serves this entity" now lives in MyrestResourceLocator and is answered from the resource plugin definitions: a resource declares the bundle it serves and the entity type that bundle belongs to. A page resource may still claim one particular node, honoured only where the site named that node in its settings. Nothing can be returned that a registered resource did not declare.

The front page is skipped by the setting that names it rather than by the literal node 5, three resources now declare the bundle they serve, and the processor loses the two dependencies that moved out with the lookup.

Closes #3618250