MAGN-4396: icons for overridden methods

# Preface
Overridden methods have the same names. In this case we can't just generate icon titles just from method name.
# Solution
Create additional method `ShortenParameterType` for generating icon titles. `ShortenParameterType` will be called, if it wasn't found any icon by default.
Also added test for this method.

## Note
I'm not sure, that I have created understandable variable names... But I tried, if you find these names strange, please, feel free to criticize it.

# Reviewers
@Benglin, please take a look.

Link to YouTrack:
[MAGN-4396 DUI: icons for overridden methods](http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-4396)
Old PR: https://github.com/DynamoDS/Dynamo/pull/2310
Please make the above more readable (with less conditions and checks):

```cs
protected virtual string GetResourceName(ResourceType resourceType, bool disambiguate = false)
{
    if (resourceType == ResourceType.SmallIcon)
        return disambiguate? ShortenParameterType() : this.Name;

    return string.Empty;
}
```