Automatically fetch on-chain IDL

[acheroncrypto]

Playground already generates UI for interacting with programs that have Anchor IDL(either built inside playground or uploaded the file manually) but it doesn't fetch on-chain IDLs.

Playground should check the program id to see if there is an Anchor IDL on-chain. This not only would allow anyone to easily interact with all programs with on-chain IDL without manually uploading it to playground, but since playground also works with localhost, it would also make the local development experience smoother.

[dhruvsol]

@acheroncrypto the fetchIDL function in anchor can be used?

[acheroncrypto]

@acheroncrypto the fetchIDL function in anchor can be used?

Yes, that's the best way. Ideally we would only fetch the IDL once user has put a custom program id from Program Credentials. And we could also add a Fetch IDL button under the IDL setting for manual fetching.