Improve representation of static/declared types in getHover response from analysis server #34196

Given some code like this:

final a = _getAnimal();

if (a is Horse) {
  print(a.showSize);
}

Inside the if block the variable a has a static type of Horse (yay!). However, the elementDescription returned by the server is just Animal a so it's not clear from the tooltip that analysis is treating this as a Horse.

The actual server response looks something like this:

{
	"id": "36",
	"result": {
		"hovers": [
			{
				"offset": 6559,
				"length": 6,
				"elementDescription": "Animal a",
				"elementKind": "local variable",
				"isDeprecated": false,
				"staticType": "Horse"
			}
		]
	}

The staticType is available here. However in the case where matches the declared type (for ex. a standard String) the field is still populated. Since the declared type is embedded inside the elementDescription property it's hard for an editor to display this information well (to avoid redundancy, we'd have to parse elementDescription up).

Some possible options suggested by @bwilkerson in Dart-Code/Dart-Code#1160 (comment) are:

1. Split elementDescription into its two parts (declared type and name)
2. A single "description" field that combines all of this information to display to the user
3. Omit the staticType if it's redundant (already in elementDescription)

Also:

We need to think about cases where there is no declared type (such as var x = ...), cases like the one above where the declared and static type are significantly different (Object vs Instance), and cases where the static type is just a refinement (List vs List<String>). And, of course, we shouldn't forget the cases where the variable isn't declared at all.