Actually use diffTracker values for display to the user.

[rtibbles]

Summary

Description of the change(s) you made

• Makes the use of the diffTracker to generate getter values actually find the values in the diffTracker (where they are keyed by node id, and then the key for the property) rather than just keying directly by the property
• This should fix the apparent editing lag that was observed by @sairina in her recently merged Edit modal - add accessibility field #3366
• This issue was originally introduced in 599e338

Manual verification steps performed

1. Check an accessibility checkbox
2. See it be immediately checked

[sairina]

Out of curiosity, why use Object.prototype.hasOwnProperty.call()? Does this have to do the this.diffTracker[node.id] object having to use call from the prototype?

[rtibbles]

hasOwnProperty is the best method for determining if a Javascript object actually has a property in itself (and it's not inherited from a parent type) - so it's the best way of telling if we have actually assigned e.g. this.diffTracker[node.id] = {}.

In theory you could call it like this: this.diffTracker.hasOwnProperty(node.id) because it is just a method of any Object that inherits from or is instantiated from the Object constructor. The reason for using the Object.prototype.hasOwnProperty.call is to ensure that the method has not been maliciously overwritten on the object itself - we have a linting rule https://eslint.org/docs/rules/no-prototype-builtins that guards against this - by calling it directly from the Object prototype we guard against it having been overwritten from JSON data or somesuch. It is probably not a real concern in this instance, but simpler to obey the linting rule.

[sairina]

Manual testing works for the accessibility checkboxes!