Remove this-escape compiler warnings

[jmehrens]

The compiler is report multiple "this-escape" warnings under JDK 21. The warning is especially chatty because it can be reported against the constructor and a calling method resulting in multiple warnings per site. This extra noise can make it a challenge to find other warnings.

The approach taken will be to:

1. Fix or update code to make it less vulnerable. Easy examples are using a different super constructor or using a super instance method call instead of this instance method call.
2. Suppress warning when dealing with classes that are designed to throw or invoke an method that can be overridden. These classes would not be updated to value types anyway.
3. Add at override annotations that are missing for classes that are modified.
4. Suppress terminal digit warning on module name for pop3 as that is the name of the protocol.
5. Suppress warning for fall through that are missing for classes that are modified and comment fall through cases.
6. Add at deprecated to methods that are deprecated via javadoc for classes that are modified.
7. Add serial ids to demo classes to get rid of those warnings.
8. Fix some raw type warnings for classes that are modified.