Improve Node Field Query API

[CoolSpy3]

Description
Allows accessing the internal fields of a proto hierarchy from a supervisor controller. There's still a lot of work to be done to integrate this into Webots, but now that I have a working proof-of-concept, I'm opening this PR to keep track of the remaining tasks.

This PR introduces the following new supervisor API functions:

• wb_supervisor_node_get_proto
• wb_supervisor_proto_get_type_name
• wb_supervisor_proto_get_parent
• wb_supervisor_proto_get_field
• wb_supervisor_proto_get_field_by_index
• wb_supervisor_proto_get_number_of_fields
• wb_supervisor_proto_is_derived

These act on the new type WbProtoRef.

Additionally, the following function has been added for WbFieldRef objects:

• wb_supervisor_field_get_actual_field

Finally, the following functions have been renamed for clarity:

• wb_supervisor_node_get_proto_field -> wb_supervisor_node_get_base_node_field
• wb_supervisor_node_get_proto_field_by_index -> wb_supervisor_node_get_base_node_field_by_index
• wb_supervisor_node_get_number_of_proto_fields -> wb_supervisor_node_get_number_of_base_node_fields

UPDATE (Aug 19): After looking through the usages of the above methods, I've noticed that the wb_supervisor_node_get_field (and related) methods are used much more than the proto variants. Thus, I've decided to keep its functionality the same in order to minimize the amount of code that will need to be updated in existing controllers. I've renamed the other methods appropriately (and updated the above text). To see the originals, check the edit history of this comment.

Related Issues
This pull-request fixes issue #6354.

Tasks

• Allow Webots to keep track of internal proto parameters
• Allow internal proto parameters to be accessed from the C supervisor API
• Ensure that updates to internal proto fields are propagated to the supervisor
• Add tests for the new API methods
• Propagate supervisor API changes to other languages
  • Update the C++ API
  • Update the Java API
  • Update the Python API
  • Update the Matlab API
  • Update WbLanguage.cpp with the new api methods
• Update references to the renamed API methods throughout the codebase
• [ ] Add a sample usage demo After looking at the existing samples, I found that there is currently no sample for and of the wb_supervisor_node_get_proto_field methods. Thus, I'm not sure what I good sample for a purely introspective API would look like. For the moment, I'll assume that the advice to write samples is indented for more simulation-facing features (e.g. devices).
• Update ROS
  • Update the ROS Controller (Improve Node Field Query API webots_ros#151)
    • Add services for the new API methods & update existing services
    • Add tests for the new API methods
  • [ ] Update the ROS2 Controller (Looks like this is automatically done by an action)
    • [ ] Update the webots submodule
• Update the documentation
  • Update documentation relating to the renamed methods and clarify the distinction between them
  • Add documentation for the new API methods
• Update the changelog

Documentation
Supervisor API

[brettle]

Also, for whomever ends up reviewing this, do you think WbNode.cpp:1795 could delete field references being held by WbNodeProtoInfo? It seems like it might, but I haven't yet found a test case that causes that behavior to occur (that includes running the current tests [which should cover all scenarios] with hidden fields [instead of normal/unconnected fields]). I would think using a hidden field in SolidProtoHierarchyInternal would cause this, but it doesn't. (Conversely, the tests fail without the current change to WbNode:1782). If you don't want to investigate, I'm happy enough with saying "the tests should cover all use cases" and seeing if a bug pops up later.

I'm ok with relying on the test coverage.

[brettle]

Excellent work!

[brettle]

@omichel, I've reviewed and approved but am not a maintainer so you, or someone else who is, needs to approve in order to get it merged.

[omichel]

Thank you!
And thanks also to @brettle for the nice review!