Investigate updateExistingComponentValues to maybe not require component deselect / reselect.

Postponed on 📌 Follow-up for #3541037: Contextual panel flickers when linking prop to field Active

Overview

It has been necessary for updateExistingComponentValues, when updating a selected component, to first deselect it.

In issue #3548320, we found a way around this specifically when linking component props to entity fields. This can be found in
updateExistingComponentValuesForLinking, which is very similar to updateExistingComponentValues.

However, the exact logic in updateExistingComponentValuesForLinking does not seem to fully work for scenarios where prop-and-field-linking isn't happening. With other value updates, the form itself does not change.

This isn't as urgent as it was for linking components, as other uses of updateExistingComponentValues would not be invoked while working with the actual form.

Proposed resolution

User interface changes

Steps to reproduce

1. Replace the logic in updateExistingComponentValuesForLinking into updateExistingComponentValues
2. Enable canvas_test_extension
3. Insert a hero in the layout
4. In the text extension, click "Update the heading value of the selected hero component"
5. The logic we added from step 1 fails to update the form.

👆 Please note the above is not a bug - the current logic in updateExistingComponentValues successfully updates everything. What is being pointed out here is that when we replace that logic with the similar updateExistingComponentValuesForLinking, it doesn't work. It would be nice to get it working, because it eliminates the need for the flicker-y deselect & reselect.