add getName method to element types

[sbatson5]

What's in this PR?

I'm currently learning craft while building a plugin for my company. Working with elements, there have been a few things I've run into that haven't seemed immediately obvious. When editing elements via the provided template:

{% extends '_layouts/elementindex' %}
{% set title = 'Products' %}
{% set elementType = 'ns\\prefix\\elements\\Product' %}

I noticed the first column wasn't showing the id as I expected. It wasn't until I stumbled on fef75e1#diff-0cf13e6e9757a569110e508f362ad1a9R482
that I realized I could update __toString() to return what I wanted.

This felt non-obvious and I felt like I was potentially overwriting a method that could be used elsewhere. So, I thought it would be nice to have a convenience method getLinkText() (happy to rename it if people feel this name is no good).

This method would just return $this->__toString() by default, so it shouldn't break any existing plugins that overwrite __toString() already to accomplish this. But it would allow us to update just that text without overwriting the method we get from the PHP base class.

[brandonkelly]

Overall looks good, but please see my comments. Also, this PR should be made for the 3.2 branch rather than develop, as we wouldn’t introduce a change like this in a 3.1.x build release.

[sbatson5]

Thanks @brandonkelly! Updated and targets to 3.2

[brandonkelly]

Thanks!