feat: Adding base game All players spawned event for exiled

[MS-crew]

Description

Describe the changes
Added a new AllPlayersSpawned event to EXILED. This event is triggered after all players have spawned at the start of a new round.

What is the current behavior? (You can also link to an open issue here)
There was no event to detect when all players had fully spawned at the beginning of a round.

What is the new behavior? (if this is a feature change)
Developers can now subscribe to the AllPlayersSpawned event to run code immediately after all players are ready at round start.

Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)
No, this is a non-breaking feature addition.

Other information:
None.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentations

Submission checklist

• I have checked the project can be compiled
• I have tested my changes and it worked as expected

Patches (if there are any changes related to Harmony patches)

• I have checked no IL patching errors in the console

Other

• Still requires more testing

[MS-crew]

@louis1706 can you revert this, mistakenly targeted the master