HITL - Add buttons and modal dialog boxes.

[0mdc]

Motivation and Context

This change introduces networked UI elements. A button and modal dialog boxes are added.

dialogue-2024-05-15_09.46.42.mp4

How it works

UI elements follow the immediate mode GUI pattern. They are both keyframe consumers and message producers.

How buttons work:

1. Server creates a button named X and sends it to the client.
2. Client receives it, renders it, and stores whether it was clicked.
3. Client sends back X's state.
4. Server checks whether X was clicked.

Notes

• Dialogue boxes are simply containers of UI elements (right now only supporting buttons).
• A UI wrapper will be created. For the sake of simplifying deltas, this will be done in a later changeset.

Related to:

• Add UI buttons and modal dialog boxes. 0mdc/siro_hitl_unity_client#26

How Has This Been Tested

Tested in multiplayer HITL application.

Types of changes

• [Development]

Checklist

• My code follows the code style of this project.
• I have updated the documentation if required.
• I have read the CONTRIBUTING document.
• I have completed my CLA (see CONTRIBUTING)
• I have added tests to cover my changes if required.