Add filters for each constraint type.

[misaki-eymard]

Currently, it is not possible to filter the contents displayed under the "Constraints" node in the tree view to include only specific constraints. It would be useful to have a filter that allows you to display only certain types of constraints when you want to change their properties in bulk. For example, you could display only physics constraints and then change specific physics parameters in bulk.

Related forum thread:
https://esotericsoftware.com/forum/d/28968-%E5%B8%8C%E6%9C%9B%E5%9C%A8%E5%B1%82%E7%BA%A7%E6%A0%91%E7%AD%9B%E9%80%89%E5%99%A8%E5%86%85%E6%B7%BB%E5%8A%A0%E5%90%84%E7%A7%8D%E7%BA%A6%E6%9D%9F

[NathanSweet]

We can do this, but dragging for constraint order should probably be disabled when the tree is filtered. Though currently we allow dragging when the tree is filtered using text search, and that seems to work.