Add example semantic tokens server

Description (e.g. "Related to ...", etc.)

This adds an example semantic tokens server, replacing the existing half implementation we have in the json_server.py example. That said, it's still only semantic tokens "level one" - there is still the range based method and delta updates to consider! :sweat_smile:

Unlike most other methods semantic tokens are quite obtuse, for example, here is the result the server sent when highlighting the code in the above screenshot

{"id": 2, "jsonrpc": "2.0", "result": {"data": [0, 0, 4, 0, 0, 0, 5, 9, 5, 8, 0, 9, 1, 3, 0, 0, 1, 1, 1, 0, 0, 1, 1, 3, 0, 0, 2, 1, 1, 0, 0, 1, 1, 3, 0, 0, 2, 1, 1, 0, 0, 1, 1, 3, 0, 0, 2, 1, 1, 0, 0, 1, 1, 3, 0, 0, 2, 1, 3, 0, 0, 2, 1, 3, 0, 0, 1, 1, 4, 0, 0, 1, 1, 3, 0, 0, 2, 1, 1, 0, 0, 1, 1, 3, 0, 0, 2, 1, 4, 0, 0, 1, 1, 3, 0, 0, 2, 1, 1, 0, 0, 1, 1, 3, 0, 0, 2, 5, 4, 0, 0, 5, 1, 3, 0, 0, 2, 1, 1, 0, 0, 1, 1, 3, 0, 0, 2, 6, 4, 0, 0, 6, 1, 3, 0, 0, 2, 1, 1, 0, 0, 2, 1, 3, 0, 1, 0, 4, 0, 0, 0, 5, 6, 5, 8, 0, 6, 1, 3, 0, 0, 1, 1, 1, 0, 0, 1, 1, 3, 0, 0, 2, 1, 1, 0, 0, 1, 1, 3, 0, 0, 2, 1, 1, 0, 0, 1, 1, 3, 0, 0, 2, 1, 3, 0, 0, 2, 9, 5, 0, 0, 9, 1, 3, 0, 0, 1, 1, 1, 0, 0, 1, 1, 3, 0, 0, 2, 1, 1, 0, 0, 1, 1, 3, 0, 0, 2, 1, 1, 0, 0, 1, 1, 3, 0, 0, 2, 1, 1, 0, 0, 1, 1, 3, 0, 2, 0, 2, 0, 0, 0, 3, 4, 2, 8, 0, 4, 1, 3, 0, 0, 1, 4, 1, 0, 0, 4, 1, 3, 0, 0, 2, 9, 5, 0, 0, 9, 1, 3, 0, 0, 2, 2, 3, 0, 0, 3, 4, 1, 0, 0, 4, 1, 3, 0, 0, 1, 5, 1, 0, 0, 6, 1, 3, 0, 0, 2, 4, 1, 0, 0, 4, 1, 3, 0, 0, 1, 6, 1, 0, 2, 0, 2, 0, 0, 0, 3, 6, 2, 8, 0, 6, 1, 3, 0, 0, 1, 4, 1, 0, 0, 4, 1, 3, 0, 0, 2, 9, 5, 0, 0, 9, 1, 3, 0, 0, 2, 6, 1, 0, 0, 6, 1, 3, 0, 0, 2, 5, 5, 4, 0, 5, 1, 3, 0, 0, 2, 2, 3, 0, 0, 3, 4, 2, 8, 0, 4, 1, 3, 0, 0, 1, 4, 1, 0, 0, 4, 1, 3, 0, 0, 2, 1, 3, 0, 0, 2, 6, 1, 0]}}

So this PR also includes an accompanying how to guide containing some interactive demos that (hopefully!) help explain what's going on

Code review checklist (for code reviewer to complete)

[ ] Pull request represents a single change (i.e. not fixing disparate/unrelated things in a single PR)
[ ] Title summarizes what is changing
[ ] Commit messages are meaningful (see this for details)
[ ] Tests have been included and/or updated, as appropriate
[ ] Docstrings have been included and/or updated, as appropriate
[ ] Standalone docs have been updated accordingly

Automated linters

You can run the lints that are run on CI locally with:

poetry install --all-extras --with dev
poetry run poe lint

openlawlibrary / pygls