Mutables for the Tree 🎄 + clean up TreeItem observers and mutables properly (#6032)

* fix: refresh object after conflict error

* fix: recover from error thrown during create

- Ensure that the "Saving" modal dialog is closed

- Notify user of the error, and also print to console to catch in e2e

* fix: default selector tree item to 'mine' folder

- If create fails due to a conflict or otherwise, and the user immediately tries to "Create" again, default the selector tree's selected item to the "mine" folder (which we know exists).

* fix: don't listen to composition if Selector Tree

* refactor: remove dead code

* fix: use MutableDomainObjects in the tree

- Only use mutables and observers if NOT a SelectorTree

- Properly clean up observers and mutables when a parent item is removed from the tree

* test: verify conflicts don't break object creation

* test: verify dialog closes and object is created

* refactor(e2e): update test

- Error notification on 'My Items' folder missing was removed, so don't check for it

* test: increase timeout

* refactor(e2e): use Promise.any()

* refactor(e2e): use Promise instead of polling

* test: add 2p annotation

* test: use `waitForRequest` instead of promise

- tidy up test, add comments describing our pattern

* docs(e2e): add best practices for network tests

* refactor(e2e): avoid using Promise.any

* fix: de-reactify observer and mutable maps

* fix: destroy by path on treeItem close

* fix: don't refresh for synchronized objects

* docs: fix a typo 🔥

* fix: remove existing mutable before adding

* fix: fail fast if these aren't functions

- Remove check for typeof 'function' to not hide any potential coding errors

* fix: walk up navigationPath if item not found

* chore: fix lint errors

* fix: parse conflicted object name correctly

* fix: re-throw conflict error

* fix: Cancel edit mode on conflict

e2e/README.md

@@ -276,14 +276,36 @@ Skipping based on browser version (Rarely used): <https://github.com/microsoft/p
   - Leverage `await page.goto('./', { waitUntil: 'networkidle' });`
   - Avoid repeated setup to test to test a single assertion. Write longer tests with multiple soft assertions.
 
-### How to write a great test (TODO)
+### How to write a great test (WIP)
+
+- Use our [App Actions](./appActions.js) for performing common actions whenever applicable.
+- If you create an object outside of using the `createDomainObjectWithDefaults` App Action, make sure to fill in the 'Notes' section of your object with `page.testNotes`:
+
+  ```js
+  // Fill the "Notes" section with information about the
+  // currently running test and its project.
+  const { testNotes } = page;
+  const notesInput = page.locator('form[name="mctForm"] #notes-textarea');
+  await notesInput.fill(testNotes);
+  ```
 
 #### How to write a great visual test (TODO)
 
+#### How to write a great network test
+
+- Where possible, it is best to mock out third-party network activity to ensure we are testing application behavior of Open MCT.
+- It is best to be as specific as possible about the expected network request/response structures in creating your mocks.
+- Make sure to only mock requests which are relevant to the specific behavior being tested.
+- Where possible, network requests and responses should be treated in an order-agnostic manner, as the order in which certain requests/responses happen is dynamic and subject to change.
+
+Some examples of mocking network responses in regards to CouchDB can be found in our [couchdb.e2e.spec.js](./tests/functional/couchdb.e2e.spec.js) test file.
+
 ### Best Practices
 
 For now, our best practices exist as self-tested, living documentation in our [exampleTemplate.e2e.spec.js](./tests/framework/exampleTemplate.e2e.spec.js) file.
 
+For best practices with regards to mocking network responses, see our [couchdb.e2e.spec.js](./tests/functional/couchdb.e2e.spec.js) file.
+
 ### Tips & Tricks (TODO)
 
 The following contains a list of tips and tricks which don't exactly fit into a FAQ or Best Practices doc.