Assets audit tests

These are edit mode tests that are intended to check basic configuration of objects. These represent actions that a non technical person could check in the editor (given a basic checklist) without needing to look at any code. Examples include making sure no prefabs have missing scripts, making sure all tile prefabs are within a certain size range, all asset data references are not null etc.

Asset audits have been configured as parameterized tests, so it will be immediately clear which object is causing failures.

Note that a business rule is that test failures for prefabs should be resolved before test failures for scenes, because the scenes may be broken because the prefabs in them are broken.