Hi,
Why did you start a new SonarQube language plugin? Which feature do you want to add to your plugin?
There's no SonarQube API which is directly related to a parser.
As mentioned in the documentation you found, SonarQube API can be fed with:
- issues against coding rules
- metrics
- coverage
- syntax highlighting
- symbol highlighting
- CPD (Copy-Paste Detector) tokens
- (...maybe something else which I forgot)
Don't try to "add the grammar and the parser to the plugin".
Try to implement one of the above features based on your parser.
It will be easier to help you when you have more precise questions.
Good luck!
Pierre-Yves