Add support for GameObject tags

[oliverbooth]

Similar to Unity's tag system, game objects should support tags so that related objects can be grouped together.

The simplest approach to achieve this would be to just have each GameObject support a Tag property - or Tags (to support more than one tag) which can be freely reassigned. However, this can lead to string dependencies and mistakes through typos which is a common mistake made in Unity.

An alternative approach would be to use a 64-bit tag mask which means tags can be stored as a single bit within the mask, rather than a collection of heap-allocated strings. This would lead to a performance boost but would in fact limit game objects to only having 64 tags maximum. Too many? Not enough?

[oliverbooth]

Provisional implementation introduced with 4f49b71

Subject to API change, issue remains open for now