Material batching: reduce redundant `Material::Bind` invocations

[adriengivry]

Problem this feature should fix
Material::Bind is being called for each draw call, even in cases where 2 entities using the same material are drawn consecutively.

Expected solution
We should implement a solution to avoid redundant Material::Bind invocations in 2 steps:

1. If the material isn't changing for n numbers of draw calls, keep it bound and don't re-bind it for every draw call
2. Batch/reorder opaque draw calls to limit Bind/Unbind call count.