Supports 12 textures on one single mesh-terrain via a texture-array-based shader.

[zwcloud]

• [x] albedo https://github.com/zwcloud/MeshTerrainEditor/commit/23ae68044b140262f422d99312080f9837a7836c
• [x] normal https://github.com/zwcloud/MeshTerrainEditor/commit/d2ec7ef693316482d1d1611b3f58ce94088b8531
• [x] a more flexible texture channel packer: pack any channel in any order https://github.com/zwcloud/MeshTerrainEditor/commit/d7978d0a9484f60d6b5f44d5b54c403097f697c0
• [x] a texture packer to create a packed texture from smoothness/roughness(R)/normal(GB)/ambient-occulsion(A) textures: https://github.com/zwcloud/MeshTerrainEditor/commit/5aac45c4db5d9648647c843ecf080de6991aae1d
• [x] update 12-textures shaders to use an albedo(RGB) texture and a merged roughness(R)/normal(GB)/ambient-occulsion(A) texture
• [x] add normal intensity to 12-textures shaders
• [x] support switch between 2/3/4, 5/6/7/8, 9/10/11/12 layers in Shader UI
• [x] creator
• [x] converter https://github.com/zwcloud/MeshTerrainEditor-issues/issues/178
• [x] fix bug: assign texture to array settings cause duplicated assignment https://github.com/zwcloud/MeshTerrainEditor/commit/aabc3e5822583c3e3461e4e49d86aa1e1582b592

Future work will be tracked in #199.

[zwcloud]

Implemented 12 Textures shader(albedo only) and corresponding editor (unstable) at zwcloud/MeshTerrainEditor@23ae68044b140262f422d99312080f9837a7836c