feat(nui/resources): add DOES_DUI_EXIST

[DaniGP17]

Goal of this PR

I don't know how this PR can be received, but I think it's a good idea to add this native to check if a dui handle is valid, because currently there is no way to do this, and when using the IS_DUI_AVAILABLE native with a handle that has been destroyed or invalid it shows an error: SCRIPT ERROR: invalid handle.
This native would be equivalent to the DOES_ENTITY_EXIST for entities.

How is this PR achieving the goal

Checking if the DUI handle is valid by verifying its presence in g_ScrBindPool.Handles.

This PR applies to the following area(s)

FiveM, Natives

Successfully tested on

Platforms: Windows

Checklist

• Code compiles and has been tested successfully.
• Code explains itself well and/or is documented.
• My commit message explains what the changes do and what they are for.
• No extra compilation warnings are added by these changes.