feat(arborist): add the ability to filter/scope by nodes

[darcyclarke]

Problem statement

Adding the ability for Arborist to filter/scope its operations to a specific part of the graph unblocks the workspace improvements & allows for future innovation in this space.

Exit criteria

• Arborist.loadActual() supports filtering/scoping by node(s)
• Arborist.loadVirtual() supports filtering/scoping by node(s)
• Arborist.buildIdealTree() supports filtering/scoping by node(s)
• Arborist.reify() supports filtering/scoping by node(s)
• Tests are written validating this behavior
• Documentation is updated to identify these methods support this new arg/behavior