[Commands] Add entity variable command (#3345)

* [Commands] Add entity variable commands

# Commands
- Add `#clearentityvariables` to clear all entity variables from yourself or your target.
- Add `#deleteentityvariable [Variable Name]` to delete an entity variable from yourself or your target.
- Add `#setentityvariable [Variable Name] [Variable Value]` to set an entity variable for yourself or your target.
- Add `#viewentityvariables [Search Criteria]` to view your or your target's entity variables.

# Notes
- `#setentityvariable` can use multi-word names/values by using double quotes like `#setentityvariable "Test Variable" "Test Value"`.
- `#viewentityvariable` does not require a search criteria, not using one shows all entity variables on yourself or your target.

* Update viewentityvariables.cpp

* Unnecessary parameter.

* Consolidate commands.

* Update entityvariable.cpp

* Update command.cpp

* Proper arguments.

zone/gm_commands/exptoggle.cpp

@@ -21,7 +21,7 @@ void command_exptoggle(Client *c, const Seperator *sep)
 		Chat::White,
 		fmt::format(
 			"Experience gain for {} is now {}abled.",
-			c->GetTargetDescription(t, TargetDescriptionType::LCSelf),
+			c->GetTargetDescription(t),
 			is_exp_enabled ? "en" : "dis"
 		).c_str()
 	);