EMSUSD-1111 Edit routing for transform commands

[pierrebai-adsk]

Add helpers to support permissions and routing:

• Provide a helper function to check permission-to-edit in the base class of the USD implementation of the UFE 3D Transform interface.
• The helper ensures that the correct edit context is used when checking permissions.

Use helpers in transforms and commands:

• Use those helper functions to check for permission to edit in command creation.
• Use those helper functions to do the edits, in command execution.
• Add edit routing context in all transform-related edits function.
• This context queries and sets where the edits should be routed.
• In particular, it is used in the execute, undo, redo and set functions of the command base class.
• Properly check permissions for matrix commands.
• The common API, 3d Matrix Op, point instances and Maya Xform stack are done.

Permissions for point instance transform

• Make the getAttribute function of the point instance modifier base class be public.
• Same for its derived classes.
• Add helper function to check permission for point instances.
• Use it to check permissions for point instances.

Add unit tests for transform routing.

[AramAzhari-adsk]

Looks good to me.