feat(IdeIntegration): add EntryPointsManager for CommonProxy and children

[leagris]

Registers CommonProxy and its children such as ClientProxy as entry points in IDEA so they are not marked as "Unused Declaration".

[Alexdoru]

btw there is no such thing as a serverproxy, it's either a CommonProxy used for dedicated servers or ClientProxy (that extends CommonProxy) for clients

[Alexdoru]

if you see a mod with a common, client and server proxy it's a mistake there should only be common and client

[Nikolay-Sitnikov]

if you see a mod with a common, client and server proxy it's a mistake there should only be common and client

Wrong. There are a couple dedicated-server-only classes, for instance DedicatedServer and DedicatedPlayerList. If you have code that uses those classes, it must be loaded through a server proxy, since a common proxy would also get loaded on the client (since it is the superclass of the client proxy), and thus would crash.