Clip editor: clip speed and animated text

Three things that were missing while editing.

• Speed for any piece of the clip, from 0.25× to 4×, like in CapCut. Video inserts can be sped up too, and audio on the tracks follows the sped-up pieces.
• Moving text — typewriter reveal and motion for the whole time on screen: pulse, sway, float.
• Render progress shows on the Export button, in the notification and on the preview, so you know how long is left.