Define new event target for JSON, and revert option passing

For the program to be consistent, the 'EventListener' target that we
  pass to a Project should be responsible for the output format.
  Otherwise, we are contingent on developers to remember passing the
  option at call-site. Plus, it overloads the project code with an extra
  boolean option.

  Instead, since the behaviour is solely driven by the execution
  context, we can instantiate a different event target upfront, and
  simply hold on to it throughout the program.

  As a nice side-effect, we can gently re-organize the code to keep the
  terminal printing logic and the json printing logic separate.

crates/aiken-lsp/src/server/lsp_project.rs

@@ -38,7 +38,6 @@ impl LspProject {
             PropertyTest::DEFAULT_MAX_SUCCESS,
             Tracing::verbose(),
             None,
-            false,
         );
 
         self.project.restore(checkpoint);