[lworld] Adopt `primitive' as the modifier in declaration of identity free classes in lieu of `inline`

The "Primitive Objects" JEP (https://openjdk.java.net/jeps/8251554) proposes a completely new nomenclature for identity free classes. Rather than being declared with inline as the modifier, these are now to be declared as primitive classes.

This RFE is to adopt the new nomenclature in sources and tests.

The said JEP also has various other changes that need to be implemented (PrimitiveObject interface for example.) These will be taken up in separate tasks.

Also the present ticket is just being used to implement support for the new declaration syntax and adapt all component's tests accordingly. Attendant changes to internal and external API's, comments, javadoc and other such will be taken up separately.