GC-Free group iterator

[Sword352]

This pull request inlines all of the methods from FlxTypedGroupIterator to ensure there are no object allocation when looping through a group.
This is a common practice taken by Haxe developers, and it's quite good hygiene to reduce GC pressure notably if you are looping through a group each frames.

I tried this change with the following code:

var group = new FlxGroup();
var memberId = 0;

for (member in group)
{
	member.ID = memberId++;
}

Here are the following JS and C++ output without this change:

var group = new flixel_group_FlxTypedGroup();
var memberId = 0;
var member = new flixel_group_FlxTypedGroupIterator(group.members,null);
while(member.hasNext()) {
	var member1 = member.next();
	member1.ID = memberId++;
}

cpp:

::flixel::group::FlxTypedGroup group =  ::flixel::group::FlxTypedGroup_obj::__alloc( HX_CTX ,null());
int memberId = 0;
{
	::Dynamic filter = null();
	::flixel::group::FlxTypedGroupIterator member =  ::flixel::group::FlxTypedGroupIterator_obj::__alloc( HX_CTX ,group->members,filter);
	while(member->hasNext()){
		::flixel::FlxBasic member1 = member->next().StaticCast<  ::flixel::FlxBasic >();
		memberId = (memberId + 1);
		member1->ID = (memberId - 1);
    }
}

(NOTE: for the C++ output I removed the HXLINE calls as it took a lot of place.)

Here is the JS output with this change (the C++ output is a bit long, but I can send it if required):

var group = new flixel_group_FlxTypedGroup();
var memberId = 0;
var _g__groupMembers = group.members;
var _g__filter = null;
var _g__cursor = 0;
var _g__length = _g__groupMembers.length;
while(true) {
	while(_g__cursor < _g__length && (_g__groupMembers[_g__cursor] == null || _g__filter != null && !_g__filter(_g__groupMembers[_g__cursor]))) ++_g__cursor;
	if(!(_g__cursor < _g__length)) {
		break;
	}
	while(_g__cursor < _g__length && (_g__groupMembers[_g__cursor] == null || _g__filter != null && !_g__filter(_g__groupMembers[_g__cursor]))) ++_g__cursor;
	var member = _g__cursor < _g__length ? _g__groupMembers[_g__cursor++] : null;
	member.ID = memberId++;
}

As you can see, the iterator has been fully inlined and no longer causes it to be allocated.

[Geokureli]

Thanks, can't believe we forgot to inline those