Improved grammar for kotlin

[per-steinar]

Context

This PR improves the Kotlin grammar by implementing additional TM-scopes

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

[per-steinar]

There are posted several screenshots of before and after applying the PR in https://github.com/redhat-developer/vscode-java/pull/3407

[donat]

Thank you for the contribution!