1.3b Update - More Fixes

Changes:

• PaperBoneAttachment3D flip rotation calculations have been corrected.
  
• New `invert_x_scale_when_flipped` property introduced to PaperBoneAttachment3D that inverts the scale of the attachment on the x-axis when flipped.
• Fixed bug that PaperPolygon2D's visibility toggle would not be reflected on equivalent meshes on startup due to a neglection to set that property upon instantiation.
• PaperPolygon2D's 3D mesh instance's visibility toggle now uses `is_visible_in_tree()` instead of `visible` for more reliable visibility toggles. Its visibility can now be toggled as a group when placed under a child of a node that's not visible.
• Fixed next pass parameters in the inspector so that they're no longer grouped with the previous shader's uniform groups.