feat(Server): add a setter for maxPlayers

[cooldogedev]

Introduction

This PR allows plugins to modify the server's max players count during runtime

Relevant issues

Changes

API changes

Added Server::setMaxPlayers(int $maxPlayers): void

Behavioural changes

Backwards compatibility

Follow-up

Tests

I tested this PR by doing the following (tick all that apply):

• Writing PHPUnit tests (commit these in the tests/phpunit folder)
• Playtesting using a Minecraft client (provide screenshots or a video)
• Writing a test plugin (provide the code and sample output)
• Other (provide details)

[SOF3]

note that this is a BC break, e.g. for plugins that do a SplFixedArray($server->getMaxPlayers())

[dktapps]

does anyone do that?

[BrandPVP]

there is no bc break because there is no such plugins that call setMaxPlayers()

[Wraith0x10]

rip i was about to make a pr doing this too 🙏