Create a Bidirected Class for Graphs

## 🚀 Feature
Create a dgl.bidirectedGraph() or dgl.bidirectedHomogenousGraph() class to make it easier for the end users to create a bi directed homogenous graph instead of doing the same steps every single time

## Motivation
Graphs in dgl are all directed. For data that is homogenous and bidirected, you need to create both the directions of the graph. This is done using the `dgl.to_bidirected()` method. So the users have to actually do this everytime they need to create it. Instead, what if we can just build a class that does that for users?

Traditionally, there are many packages that do this for the users
e.g. fastAI package has built dataloaders for the users to ingest data from multiple types (csv, image data from multipel folders of each class etc)

Therefore, rather than asking the users to remember the bidirectionality everytime, can we create a class for them built on top of existing DGL methods to make it easier

## Alternatives

create a dgl graph and then call the to_bidirected() method everytime

## Pitch

## Additional context