To develop the Robot Framework Language Server for Intellij, download the sources
and head to the robotframework-intellij directory (where gradlew is located).
Then, verify if everything is ok by running the tests with: gradlew test (note:
a python executable must be in the PATH).
Afterwards, it should be possible to just open the robotframework-intellij folder
in Intellij (the community edition is Ok).
Note that robotframework-intellij is mostly the integration of the Robot Framework Language Server
into Intellij and the actual implementation of most features reside in the
Robot Framework Language Server itself.