MSI Refactoring

[Avery-Dunn]

Refactoring the codebase to better accommodate the new MSI code. The main goals of this PR:

• Make no changes to the functionality or visibility of any API that MSAL Java has already released, and do not break any of the newer MSI-related tests
• Add a new IApplicationBase interface above the existing IClientApplicationBase, to have better control over the visibility of APIs for the managed identity application vs. the existing public/confidential client applications (commit 3715e77)
• Refactor the new MSI-related classes to better follow Java best practices for naming/visibility/etc., and match the coding styles used throughout the rest of MSAL Java (commit 6835ef0)

[neha-bhargava]

We will also need to hide the API's at the request level. Right now the ManagedIdentityParameters implements the IAcquireTokenParamters which have APIs WithClaims, extraQueryParams etc. Which are not relevant to managed identity. Please add a base level to IAcquireTokenParameters as well.