Allow retrieving an Audio Bus instance from creation, by name, and by index.

[yosimba2000]

https://docs.godotengine.org/en/stable/classes/class_audioserver.html

You can create audio bus via add_bus, but it does not return the bus instance. You must remember the index you assigned this new bus.
You can assign a bus name via set_bus_name, but it requires the bus index.
You can retrieve the bus index via get_bus_index, but it requires the bus name.

There is no method that retrieves the actual bus instance/class.
In all cases, ONLY the bus index is used to identify a bus.
The ONLY time the bus name is even used is when assigning the set_bus_send of a bus, or assigning the bus of an AudioPlayer node.

I think the following should be done:

1. add_bus is changed to accept 2 parameters: an integer for bus index, and string for bus name. This assigns the bus index at the integer, and assigns the bus name to the string.
2. add_bus should also return the newly created bus instance.
3. a new function called get_bus_by_index that takes an integer and returns the bus instance at that index.
4. a new function called get_bus_by_name that takes a string/stringName and returns the bus instance with the matching name.
5. the bus instance itself has functions to return and modify its effects.
   (eg) Say I'm changing a reverb effect: get_bus_by_name("MyBusName").Effect(someEffectIndex).roomSize=1
6. all other get_bus___ functions like get_bus_effect are modified to accept a bus index and/or name parameter to find the bus.
7. modify remove_bus to accept both int index and bus name to delete the audio bus.

This is important because adding/deleting bus instances can affect the indices of all the other buses. And now the indices you've just memorized/stored are no longer valid. But caching bus instances or retrieving them by name solves that issue.