[Bugfix] Addressing Draggable2D UI Lag

[CG-Tespy]

Description

Bug fix

What is the current behavior?

When you try to drag a UI element with a Draggable2D component, it lags behind, moving so slowly.

What is the new behavior?

Dragging UI elements works as well as dragging regular 2D sprites does with the Draggable2D component

Important Notes

• My change modifies the runtime execution/behaviour of the Draggable2D component

Other information

• The bug came about because of how ScreenToWorldPoint doesn't play nice with how Canvases manage space. So I thought it'd be easier to have the position-updating work by caching current and previous mouse and world positions
• For better naming, I renamed the delta variable to "mouseMovement"
• For optimization, I had the main camera cached in Awake
• To make the component work with both UI images and Sprites, I had to incorporate two algorithms in this script. So we don't have to use if statements, I set up a dictionary containing them. See UpdateLocalPositionForUI and UpdateLocalPositionForSprites

[CG-Tespy]

The latest bugfix made things work off of world position again. Updated the PR OP

[CG-Tespy]

Just noticed another bug: when you have a Sprite using the Event System, the drag effect gets greatly exaggerated. I'll be looking into a solution