Refactor code to use composition API

[akhenry]

Summary

There are several instances in our codebase where domain object composition is being changed by directly mutating the composition property of domain objects. This is problematic for two reasons:

1. It will not trigger composition listeners.
2. It will not work at all with anything other than the default composition provider.

We see a lot of bugs that are some version of "removing an object from X does not update Y". This issue may underlie a lot of these kinds of issues that keep coming up. There was legacy code that used to plaster over this issue by automatically detecting composition changes in object mutation in order to bridge the legacy and current APIs, but this code has been removed along with the legacy codebase.

Expected vs Current Behavior

Object composition operations should always use the composition API.

[ozyx]

Testing Notes

Test composition in general:

1. Add / Remove objects to / from composition-able objects (particular focus on scatter plots, gauge, display layout, and flexible layout)
2. Add / Remove objects to/ from composition-able objects using the RemoveAction (selecting 'Remove' from the right-click context menu in the object tree or elsewhere)
3. Verify the composition is correct after save by calling this.openmct.composition.get(domainObject) in console

[unlikelyzero]

Verified