[REQ][Java/Scala] Migrate away from outdated joda library by default

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

Since java 8 released joda recommend to use java.time library instead (see official note https://www.joda.org/joda-time/)

For now on different java based generators we have at least 3 different implementations:

• joda.time (outdated)
• java.util.Date (deprecated)
• java.time.* (standard since java8)

Describe the solution you'd like

It would be nice to have dateLibrary property at DefaultCodegen level, or reogranize code base to have one more additional level of abstraction with AbstractJavaBasedCodegen which could be base interface for AbstractJavaCodegen, AbstractScalaCodegen, AbstractKotlinCodegen and others.

It will allow to describe final implementations with exact date libraries they support.

After all final implementations will support dateLibrary property we can set java8 library by default from the next major release and continue with migration of every final implementation

Start with DefaultCodegen and the Java/Scala generator abstractions named in the issue, then inventory their current date-library implementations. Define the supported dateLibrary options and migration scope across affected generators. Done means the abstraction and default behavior are specified for the relevant Java-based generators, with each implementation's supported libraries identified.