[MERGED] warning 24X: enum item "%s" not handled in switch

[Daniel-Cortez]

What this PR does / why we need it:

This PR adds a new diagnostic that warns the user if an item of a named enumeration is not covered by any of the switch cases, as suggested in #528.
Example:

enum EFamily
{
	FAM_GROVE,
	FAM_BALLAS,
	FAM_VAGOS,
	FAM_AZTECAS
};

stock GetFamilyColor(EFamily:family)
{
	switch (family)
	{
		// NOTE: The user forgot to add a case for "FAM_AZTECAS"
		case FAM_GROVE:   return COLOR_GREEN;
		case FAM_BALLAS:  return COLOR_PURPLE;
		case FAM_VAGOS:   return COLOR_YELLOW;
	} // warning 24X: enum item "FAM_AZTECAS" not handled in switch
	return COLOR_GREY;
}

Which issue(s) this PR fixes:

Fixes #

What kind of pull this is:

• A Bug Fix
• A New Feature
• Some repository meta (documentation, etc)
• Other

Additional Documentation: