Unity 6.5+ compilation fix

[NoixDeXydre]

With Unity 6.5 beta, CreateAssetWithContent cannot compile and needs to be replaced with CreateAssetWithTextContent.

[Lewox]

Tested it on 6000.5.1f1 and it works well, what I would do @NoixDeXydre is to squash those commits into a single one so Git history is cleaner.

[NoixDeXydre]

Tested it on 6000.5.1f1 and it works well, what I would do @NoixDeXydre is to squash those commits into a single one so Git history is cleaner.

I've just squash the two commits. It should be good now 👍

[Hinen]

I verified that ProjectWindowUtil.CreateAssetWithTextContent is not present in Unity 6000.3.11f1, while CreateAssetWithContent is still available there. Therefore, UNITY_6000_0_OR_NEWER would break compilation on Unity 6000.0–6000.4. Could you change the guard to UNITY_6000_5_OR_NEWER? I verified that version guard with a full script recompile on Unity 6000.5.10f1.