Fairy bridge demo

This shows off a potential viaduct replacement that uses new UniFFI
features. Check out `components/fairy-bridge/README.md` and
`examples/fairy-bridge-demo/README.md` for details.  Execute
`examples/fairy-bridge-demo/run-demo.py` to test it out yourself.

The UniFFI features are still a WIP.  This is currently using a branch
in my repo.  The current plan for getting these into UniFFI main is:
  - Get the `0.26.0` release out the door
  - Merge PR #1818 into `main`
  - Merge my `async-trait-interfaces` branch into main (probably using a
    few smaller PRs)

There is a C++ backend using libcurl.  I think that necko shouldn't be
any harder than this.

.circleci/config.yml

@@ -107,6 +107,7 @@ commands:
       - run: sudo apt-get install python tcl
       - run: sudo apt-get install python3-venv
       - run: sudo apt-get install libclang-dev
+      - run: sudo apt-get install libssl-dev
       - run:
           name: Install NSS build system dependencies
           command: sudo apt-get install ninja-build gyp zlib1g-dev pip