Replace XRTK custom shaders with Unity's built-in shaders

[FejZa]

XRTK - Mixed Reality Toolkit Feature Request

Is your feature request related to a problem? Please describe

I'd like to remove any custom shaders used in XRTK and replace them with Unity's built-in shaders.
This is a step in anticipation for XRTK's URP/HDRP support. Removing custom shaders will help in transitioning the toolkit to render pipelines. There shouldn't be any breaking changes here.

How would you classify your suggestion

• New platform support

Describe the solution you'd like

Remove all custom shaders so that materials can automatically be migrated to render pipelines.

[StephenHodgson]

Isn't this just a duplicate (or part of a step for) #407 ?

[FejZa]

It's definitely a step towards #407

[StephenHodgson]

Can we close this one and just use #407 as our task list?

[FejZa]

Okay, we can do that.