Release notes for 424

Changed microprofiler label "uiStep" to "frameStep", "jointsStepUi" to "stepAnimatedJoints". Added joint counts to tooltip for stepAnimatedJoints.

Added BasePart.Mass as a property. Once this is enabled we'll deprecate BasePart:GetMass() in favor of this.

Studio: Fix input methods becoming inactive after clicking on an already focused textbox

Fixed an issue by which setting the "Playing" property on a sound would result in excess network traffic even if the property did not change

Fixed an issue by which setting the "Playing" property on a VideoFrame would result in excess network traffic even if the property did not change