Generalize AST Flags to a single 4-byte flag

[Ed94]

Right now there is:

ModuleFlag ModuleFlags;
union {
	b32 IsFunction; // Used by typedef to not serialize the name field.
	b32 IsParamPack; // Used by typename to know if type should be considered a parameter pack.
	OperatorT Op;
	AccessSpec ParentAccess;
	s32 NumEntries;
};

At the end of the AST data layout. We can simplify the layout to:

CodeFlag CodeFlags;
union {
	OperatorT Op;
	AccessSpec ParentAccess;
	s32 NumEntries;
};

Where CodeFlag is an enum : u32

This would leave open the ability for others to add their own flags without much hassle.