Expand "What's New" section

The spirit of this update is to:

Slightly expand the detail on changes in 4.0
- Opted for "javax.ejb" vs "javax" as several javax namespaces referenced in the document are still valid and not renamed.
- Added short reasons for the removals so that knowledge is in the spec (vs institutional knowledge)
- Explicitly call out the fact that this specification revision is a breaking change
Explicitly add "Jakarta Enterprise Beans 3.2" as this specification is technically part of our history. Also to call out a potential source of future confusion since it has the same version number as Enterprise JavaBeans 3.2.
Use "Enterprise JavaBeans" for the duration of this section where applicable:
- Legally correct trademark to use for the older specifications
- Adds a bit of clarity by explicitly noting the name change and history at the JCP
Introduce links to EJB 3.1 and 3.0 in Related Documents as these specifications are explicitly referenced.

jakartaee / enterprise-beans