feat: action system cleanup MTT-4244

[pdeschain]

Description

This PR changes the layout, namespaces, method names and locations of files for Action system to make it a bit more legible.

• All Actions now live in Unity.Multiplayer.Samples.BossRoom.Actions namespace.
• FXProjectile was moved to GameplayObjects and out of the Actions folder because it's not directly related to Actions (albeit one of the actions spawns these projectiles).
• Methods of Action and ActionFX that had overlap with Unity event function names were changed to avoid confusion:
  • Start -> OnStart
  • Update -> OnUpdate
• Actions-related classes were sorted into folders that describe their purpose (BaseTypes, ConcreteActions, ActionPlayers, ActionInput)

Issue Number(s)

MTT-4244

Contribution checklist

• [ ] Tests have been added for boss room and/or utilities pack
• [ ] Release notes have been added to the project changelog file and/or package changelog file
• [x] Pull request has a meaningful description of its purpose
• [x] All commits are accompanied by meaningful commit messages
• [x] JIRA ticket ID is in the PR title or at least one commit message
• [x] Include the ticket ID number within the body message of the PR to create a hyperlink