Improved kotlin syntax based on latest documentation

[per-steinar]

Improved syntax based on documentation from https://kotlinlang.org/

Summary

• Improved scopes for imports
• Separating val and var
• Improved capturing of functions and parameters
• Added variable and object capturing
• Added capturing of keyword for mapping
• Added capturing of optional accessor
• Added capturing of elvis operator

See: https://github.com/eclipse/buildship/pull/1273