Improve bespoke transition animations for Safari compatibility

[yhatt]

Fix #572.

Fixed issues

• The timing of animation timing functions do not match between the outgoing slide and incoming slide
  • When animating transform property, its definitions should put into both starting keyframe and ending keyframe. If not, animation-timing-function property in starting keyframe will not work only in Safari.

• drop: The incoming slide is slipping while dropping
  • box-shadow property is seems to cause misalignment. So we are disabled shadow effect in Safari.

• rotate: Rotating animation has too showy effect
  • Use rotateY(0.0001deg) instead of rotateY(0). Using a positive vector will suppress showy animating in motion interpolation.

Other fixes for transition animations

• flip: Stopped moving rotation axis.
• rotate: Prevented overlapping slides while rotating.

Known issues

• Morphing animation by view-transition-name CSS property will not work correctly in Safari, due to force scaling by marpit-svg-polyfill to fix Safari rendering bug about SVG with <foreignObject>.