Update to Cubism 4 SDK for Unity R2

[wada-at-live2d-com]

Added

• Add Unity 2020 to the development environment.
• Add feature to make Animator Controller that supports MotionFade.
• Add a process that applies the Culling configuration from Model Data.
• Add a AnimatorController generator that is already set CubismFadeStateObserver.

Changed

• Change the setting of Player Loop customized by other assets not to be rewritten in Unity 2019.3 or later.
• Change to get the path of the audio files associated with .motion3.json from .model3.json.
• Change to enable the appropriate Cubism iOS plugin before building.
• Change the handling of UnmanagedArrayView pointers due to improve the performance. @ppcuni
• Change the default importing mode to Original Workflow.
  • Note: Importing this version into an older version SDK will override this setting.
    see Cubism SDK Manual page

Fixed

• Fix the bug of the weight calculation of MotionFade.
• Fix the bug of the weight calculation of Expression.
• Fix the bug when playing a motion that is shorter than the fade time or transitioning to a motion with a different fade value.
• Fix fixed value for the generated .exp3.asset fade value when there is no fade value in .exp3.json.
• Fix registering the delegate duplicately on calling CubismUpdateController.Refresh().
• Fix checking bounding box hit every time before checking mesh hit by @DenchiSoft.

Removed

• Remove Unity 2017 from the development environment.