Documentation for ShaderMaterial and RawShaderMaterial

Improves description of `ShaderMaterial` and `RawShaderMaterial`, as per #5411. 

I included some information from https://github.com/mrdoob/three.js/wiki/Uniforms-types, along with analogous information for attributes into the page for `ShaderMaterial`, but I left out most of the more obscure types. I can add them for completeness if preferred. 

I also incorporated stuff from https://github.com/mrdoob/three.js/issues/1188#issuecomment-3666286 into the page on `WebGLProgram` in order to have a reference in the docs to the built-in matrix uniforms.