Add Mouse Input API and test widget

[WybrenKoelmans]

Introduce a Mouse Input API along with a test widget to handle various mouse events such as clicks, double-clicks, and drags. This addition enhances interaction capabilities and provides a framework for further development of mouse-related functionalities.

[github-actions]

Integration Test Results

15 tests  ±0   6 ✅ ±0   3s ⏱️ ±0s
 1 suites ±0   8 💤 ±0 
 1 files   ±0   1 ❌ ±0 

For more details on these failures, see this check.

Results for commit 53b55fc. ± Comparison against base commit cbe4b9c.

[WybrenKoelmans]

https://discord.com/channels/549281623154229250/724293659809284137/1518316407522070599

Sprung:

my vision of how to approach this would be

• figure out what is needed to replicate engine behaviours, e.g. maybe for drag selection you'll need some spSelectUnitsInScreenRectangle. implement those
• using the above, provide widget implementations to those behaviours and put them in basecontent
• make the engine not consume any mouseclicks at all, such that gameside lua is the only client and can design the behaviour ("claiming ownership" and whatever else) any way it likes

i think the native gui (build menu, sharedialog etc) are fine not to reimplement
just selection, dragging, rightclick etc

the 2nd and 3rd steps in my list are technically not needed, in that if a game's lua always claims mouse it can already do anything it wants
just more annoying to work with probably since mouse is permaclaimed

This is offered as a reference, I will not work on this in the near future.