Begins the work described in #971

This PR fills documentation gaps and improves existing documentation to all interfaces in the library. The changes exclusively affect Javadoc comments, so there are no changes to the actual behavior of any API.

This PR is also a trial run of the new agent feature in IntelliJ's Copilot plugin:

• All of the changes were manually reviewed to ensure MSAL behavior was described accurately
• With few exceptions, the prompts produced accurate descriptions on the first try without being given any context about MSAL's actual behavior
  • For the most part, I simply told it to review all interfaces with missing/poor documentation, list them based on quality, then told it to add/improve a few filenames at a time
• The few mistakes it did make were easily corrected by a follow-up prompt describing what was wrong
  • As an example, it incorrectly implied that "scopes" API was just for Graph resources (likely because many of our tests use Graph), and I just had to tell it to give a more generic description