Simplify test results data

[ChrisC]

Closes #10 while also removing some additional IPC cruft in the way we were loading the test plans from the test files into the harness.

There was one request to in #10 to move the testId out of TestResult and into the TestPlanResult. Unfortunately, I didn't get to this, as it looks to me like it would require a bigger refactor of how we're loading the test plans via the CLI middleware. We don't actually get the test Id until later in the run process, when we JSON parse the file to run the tests. If you have a simple suggestion for making this change as requested, I'm all ears @jugglinmike ...

[jugglinmike]

I just got all sorts of confused because we don't actually use the AriaATCIData.TestPlanResult type. It looks like we just emit a modified version of AriaATCIHost.TestPlan, instead. Maybe we could extend the modification logic because we have the testId at that moment. That doesn't seem like a huge refactoring to me, but maybe I've missed something important. In either case, I'm happy to punt that to another day if you don't mind creating an issue/Task for it.

[ChrisC]

@jugglinmike I got that testId property update in the last commits. Here's some sample TestPlanResult output as of c259f16:

{
    filepath: "test-06-navBackToSlider-voiceover_macos.collected.json",
    id: "navBackToSlider",
    log: [ ... ],
    results: [
      {
        capabilities: { ... },
        commands: [
          {
            command: "ctrl+opt+left ctrl+opt+left",
            response: "128\n            Red             slider\nRed\nYou are currently on a selectable text. ",
            assertions: [
              {
                expectation: "Role 'slider' is conveyed",
                verdict: null,
              },
              {
                expectation: "Name 'Red' is conveyed",
                verdict: null,
              },
              {
                expectation: "Value '128' is conveyed",
                verdict: null,
              },
              {
                expectation: "Orientation 'horizontal' is conveyed",
                verdict: null,
              },
              {
                expectation: "Minimum value '0' is conveyed",
                verdict: null,
              },
              {
                expectation: "Maximum value '255' is conveyed",
                verdict: null,
              },
              {
                expectation: "Screen reader switched from reading mode to interaction mode",
                verdict: null,
              },
            ],
          },
          { ... },
          { ... },
        ],
      },
    ],
  },

[ChrisC]

Note that in the previous version we were inserting the string id as testId even though the type specifies that we were expecting a numeric id. I updated the types to reflect this. I'm assuming we want to stick with using the string version as the id and not the numeric presentationNumber...

[jugglinmike]

The code looks good, and it functions as expected. Thanks for doing this, @ChrisC--these patches are really making the code base smaller and more coherent!