[analytics] introduce DTDProcess

[pq]

Introduces a DTDProcess abstraction that will be used in a service that handles analytics checking and consent management.

Much of the logic is extracted from DartToolingDaemonService. Once the analytics service is implemented and proven out, DartToolingDaemonService will be refactored to use DTDProcess and the duplication removed.

Still a WIP, but client access might look something like this:

      DTDProcess dtdProcess = new DTDProcess();
      dtdProcess.setListener(new DTDProcessListener() {
        @Override
        public void onProcessStarted(@Nullable String uri) {
          JsonObject params = new JsonObject();
          params.addProperty("tool", getToolName());
          try {
            dtdProcess.sendRequest("UnifiedAnalytics.getConsentMessage", params, true, new DartToolingDaemonConsumer() {
              @Override
              public void received(@NotNull JsonObject response) {
                // Do stuff.
              }
            });
          } catch (WebSocketException e) {
            // Handle
          }
        }
      });
      dtdProcess.start(sdk);
...

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[helin24]

Looks great other than my comment