Fix wave direction in GL3+ shader

[srmainwaring]

This PR corrects the texture coordinates used to apply the wave displacements in the GL3+ shader - the y-direction was reversed.

There are a number of other minor changes to keep the metal and glsl shaders in sync.

Details

• Update y-texture coordinate in GL3+ shader (y was reversed).
• Use normal_matrix to transform normals and tangents into world space.
• Keep metal and glsl shader variable names in sync.