Fix double props when inherited from parameterized class [#1228]

[astashov]

Sometimes, when a subclass inherits a property from a parameterized
class, the property appears twice in the docs.

That happens, because (by some reason, I'm not sure why) the field
objects for those getters and setters have different references
(though they are the same - their names are the same, returning types
are the same, etc). Since FieldElementImpl doesn't override default
equality, after we added the field for getter into
_inheritedProperties, when handling setter, we compare fields of
getter and setter by reference there:

dartdoc/lib/src/model.dart

Line 479 in 38a7863

if (_inheritedProperties.any((f) => f.element == e)) {

And usually these are the same object, so we won't see 2 properties in
the generated docs. But in that case by some reason they are 2 different
objects, so we add the field of the setter as well, and then we have 2
same props in the generated docs as a result.

It seems like we can safely compare their names (since there couldn't be
2 properties with the same name in a class anyway). That would fix the
problem.

I've added that in this commit, and also a unit test covering that case.

Fixes #1228

[devoncarew]

Thanks! and lgtm

[Hixie]

We really should figure out why we're getting two setters and getters. There could be an underlying more serious bug there.

[astashov]

It's not 2 setters and getters, it's a setter and a getter have variable property, which usually returns the same object for both getter and setter, and the code relied on that. And in this edge case their variable property by some reason return different, but equal objects (they have different hashCodes).