1.4a Update - Quick Fixes and Some Internal Restructuring

Changes:

• Fixed outdated array reference in PaperPolygon2D's `update_color()` function (Thanks to Gokigenyou for pointing this out).
  
• Removed optional parameters in certain PaperPolygon2D `update` functions, due to there not really being a point in having them.
• Made `auto_params` consistent in only needing a PaperPolygon2D for any of its function parameters.
• Removed outdated flip checking in PaperPolygon2D's `update_texture()` function.
• Introduced `update_material_auto_param()` and `update_material_auto_params()` functions to PaperPolygon2D to help abstract its other update functions.
• Removed and modified multiple internal update functions in PaperSkeletonMeshManager for the sake of implementing new universal `update_auto_param_for_all_polygons()` and `update_auto_params_for_all_polygons()` functions.
• Custom z-index selection removed from PaperBoneAttachment3D. Due to how layer ordering direction is now determined by the mesh's currently viewed face, the exact z-position cannot always be reliably determined anymore, making this already rather niche feature now rather unreliable.
• Re-added some accidentally removed lines of code that updated the current flip state in PaperSkeleton, which likely would've introduced problems for PaperBoneAttachment3D's flipping logic if gone unchecked.