[Rendering] Use 16bit data types on the GPU where possible

[kanerogers]

Background

As Hotham's renderer is primarily memory bandwidth bound on the Quest 2, dropping to 16 bit data types will not only improve bandwidth, but in general only use a single instruction, compared to two, when operating on them. This could be a very significant performance increase.

TODO

• Modify Vertex struct
• Modify asset importer to convert to the correct precision
• Modify shaders

[kanerogers]

Closed in #415