[Rules] Update logic checks everywhere for FVNoDropFlag. (#2179)

* Update logic checks everywhere for FVNoDropFlag.

FVNoDropFlag == 0 is disabled
FVNoDropFlag == 1 is enabled for everyone
FVNoDropFlag == 2 is enabled for Admin() >= Character:MinStatusForNoDropExemptions

* Adding extra parenthesis to reduce ambiquity of order of operations for FVNoDropFlag checks

* Move FVNoDropFlag checks into a helper function in emu_constants.cpp and make an enum for the possible values.
Added console warning if setting is outside of allowed values.

* Move to client scoped helper method

Co-authored-by: Akkadius <akkadius1@gmail.com>

zone/client_packet.cpp

@@ -15559,3 +15559,23 @@ void Client::SetSharedTaskId(int64 shared_task_id)
 {
 	Client::m_shared_task_id = shared_task_id;
 }
+
+bool Client::CanTradeFVNoDropItem()
+{
+	const int16 admin_status             = Admin();
+	const int   no_drop_flag             = RuleI(World, FVNoDropFlag);
+	const int   no_drop_min_admin_status = RuleI(Character, MinStatusForNoDropExemptions);
+	switch (no_drop_flag) {
+		case FVNoDropFlagRule::Disabled:
+			return false;
+		case FVNoDropFlagRule::Enabled:
+			return true;
+		case FVNoDropFlagRule::AdminOnly:
+			return admin_status >= no_drop_min_admin_status;
+		default:
+			LogWarning("Invalid value {0} set for FVNoDropFlag", no_drop_flag);
+			return false;
+	}
+
+	return false;
+}