Add ability to generate a QL query from a code snippet

[aeisenberg]

• 90% of users 90% of the time, all they need is to define their sources and sinks and plop them into a Data Flow config.
• Not everyone needs to write config flows from scratch. New users often just need help writing sources and sinks.

The idea would be that a user selects a code snippet (a property, method call, etc), runs the CodeQL: Generate query command, and a new editor opens with one or more generated QL predicates that each will select the target of the snippet to greater or lesser specificity.