KeyboardDragListener: rename dragVelocity and shiftDragVelocity

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This came up during discussion about KeyboardDragListener drag speeds in #1601. It's not the first time it's come when when designing how to configure KeyboardDragListener.

In 6910117, @jessegreenberg added the current KeyboardDragListener options for controlling drag speed:

  // While a direction key is held down, the target will move by this amount in view coordinates every second.
  // This is an alternative way to control motion with keyboard than dragDelta and produces smoother motion for
  // the object. dragVelocity and dragDelta options are mutually exclusive. See dragDelta for more information.
  dragVelocity?: number;

  // While a direction key is held down with the shift modifier key, the target will move by this amount in view
  // coordinates every second. Shift modifier should produce more fine-grained motion so this value needs to be less
  // than dragVelocity if provided. This is an alternative way to control motion with keyboard than dragDelta and
  // produces smoother motion for the object. dragVelocity and dragDelta options are mutually exclusive. See dragDelta
  // for more information.
  shiftDragVelocity?: number;

Velocity is a vector; speed is a scalar. So these options are incorrecly named - they should be dragSpeed and shiftDragSpeed. Let's change them so we don't continue to have this confusion, especially since PhET is a STEM project.

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There are 28 occurrences of dragVelocity:, 29 occurrences of shiftDragVelocity:. So this looks like a relatively straightforward change. If @jessegreenberg doesn't have time to do this, and approves of the proposed change, I'll be happy to handle it.

[jessegreenberg]

Very good point! These are not vectors, "speed" sounds great.

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1/28/2024 dev meeting:

Consensus was to change to dragSpeed and shiftDragSpeed. I'll do this.

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PSA to Slack#developer:

PSA: KeyboardDragListener options are now named dragSpeed and shiftDragSpeed. Changes to repos that I am not responsible for include: balloons-and-static-electricity, friction, keplers-laws, projectile-data-lab, scenery-phet (MeasuringTapeNode), and solar-system-common.

Closing.