Support SerializedObject and SerializedProperty

E.g. Given something like

``` csharp
using UnityEngine;
using UnityEditor;

public class MyObject : ScriptableObject
{
public int myInt = 42;
}

public class SerializedProperty : MonoBehaviour
{
void Start ()
{
MyObject obj = ScriptableObject.CreateInstance();
SerializedObject serializedObject = new SerializedObject(obj);

SerializedProperty serializedPropertyMyInt = serializedObject.FindProperty("myInt");

Debug.Log("myInt " + serializedPropertyMyInt.intValue);
}
}
```
- [ ] Create a reference provider for the `"myInt"` string literal to reference the `MyObject.myInt` field, providing find usages + rename support
- [ ] The reference provider would provide a candidate list of available public fields to power code completion in the string literal
- [ ] Flow type information from the property name to the usage of the property, so that the correct accessor is used - if `myInt` is actually a string, then `serializedPropertyMyInt.intValue` will fail. It should suggest `serialisedPropertyMyInt.stringValue`

This is difficult, and would require control flow analysis. The `FindProperty` call would need to know the type of the object passed to `new SerializedObject(obj)`. And the returned `SerializedProperty` would need some "type" information attached.