[UI] Sending Data to UI Canvas Event System.

**Issue description:**
Attempting to send input data into the canvas event system.

e.g.
Canvas.GUI.MousePosition = MouseCursorScaled;

in this e.g. the MousePosition if read from the GUI is always Float2(0,0).

I need to be able to control the canvas from code as if the canvas is being used. At the current moment, I cannot seem to figure out how
This would be archived, or if it even possible with the current UI system. (dont have access to relevent API calls?)

**Flax version:**
1.6++

Start by tracing the canvas event system and the Canvas.GUI.MousePosition entry point shown in the issue. Determine whether input data can be supplied through the current UI API and document the relevant limitation or supported path; done means code-driven canvas control is established as possible or impossible.

Written by the indexing model from the issue text.