[FEATURE REQ] Add getBearerTokenProvider() method that return a callback to get token in Azure Identity

[mssfang]

Is your feature request related to a problem? Please describe.

Python and JavaScript Azure Identity SDK have a method getBearerTokenProvider that returns a callback, Supplier<String> in Java.

Python: https://github.com/Azure/azure-sdk-for-python/blob/main/sdk/identity/azure-identity/azure/identity/_bearer_token_provider.py

JavaScript: https://github.com/Azure/azure-sdk-for-js/blob/c0b9ee632230a89a54820269e133f7719cdc9f4b/sdk/identity/identity/src/tokenProvider.ts#L47

Describe the solution you'd like

We can add a similar public API in Azure Identity SDK for Java:

Supplier<String> getBearerTokenProvider(TokenCredential credential, String scope)

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