Expression widget - Autocompletion for methods obtained from suggestion db

[farmaazon]

The methods available in set component expressions are all methods of Column type, plus some internal methods defined in ExpressionVisitorImpl.java:395

• Part of this task is also starting a discussion about next steps: putting builtin functions to a designated module, for example, and what are the plans for supporting methods of other types than Column.
• Some functions are specified as having variable arg list, which is translated to call with an array

This task should be split into many PRs where possible