allow local NPC functions to be public or private

[Helianthella]

This is my proposal to fix #2137:

• local functions can no longer be called as events, even if their label begins with On
• local functions may be explicitly exported by defining them as public function ....
  this allows other scripts to call them as if they were part of their own script
• exported local functions can be called from any script by doing "npc name"::MyFunction();

-	script	npc1	FAKE_NPC,{

	private function NonExported {
		return "[1] non-exported";
	}

	public function Exported {
		return "[1] exported";
	}

	// local call:
	debugmes(NonExported()); // => [1] non-exported
	debugmes(Exported()); // => [1] exported

	// call in another NPC:
	debugmes("npc2"::NonExported()); // ERROR: not exported
	debugmes("npc2"::Exported()); // => [2] exported
}


-	script	npc2	FAKE_NPC,{

	function NonExported {
		return "[2] non-exported";
	}

	public function Exported {
		return "[2] exported";
	}

	// local call:
	debugmes(NonExported()); // => [2] non-exported
	debugmes(Exported()); // => [2] exported

	// call in another NPC:
	debugmes("npc1"::NonExported()); // ERROR: not exported
	debugmes("npc1"::Exported()); // => [1] exported
}

// local call syntax (unchanged):
<function>({<arg>...})

// public call syntax:
"<npc name>"::<function>({<arg>...})

// also:
callfunctionofnpc("<npc name>", "<function>"{, <arg>...})

[HerculesWSAPI]

This change is 

[4144]

and i think need add some tests to call local functions in CI

[Helianthella]

@4144 yes, sure, I will do this after I write the docs

[Helianthella]

@4144 I have added unit tests

[Helianthella]

moving this to the next milestone

I felt the : prefix was ugly, so I will change the syntax to

function MyFunction { … } // implicitly private
private function MyFunction { … } // explicitly private
public function MyFunction { … } // explicitly public

It's cleaner, and the public and private keywords could also be reused in the future for other things

[Helianthella]

I'll do some commit squashing once the review process is over

[Helianthella]

I added two config flags for more flexibility:

• functions_private_by_default defines whether functions are private or public when not explicitly set as public or private.
• functions_as_events allows functions to be called as events if made public. This allows for backward compatibility if someone was using this bug as a feature.

-	script	@mycommand	FAKE_NPC,{
	public function OnInit {
		bindatcmd("mycommand", "@mycommand::OnCall");
		return;
	}

	private function doSomething {
		dispbottom(getarg(0));
		return;
	}

	public function OnCall {
		doSomething(.@atcmd_parameters$[0]);
		return;
	}
}

[Kenpachi2k13]

Furthermore your commits need some squashing. ☺️

[Helianthella]

@Kenpachi2k13 as noted earlier, I do intend on squashing once the review process is done.
It makes it easier for maintainers to review incremental changes when the branch is not force-pushed