Update layout.html to support a sphinx version that is not three-integers

[pelson]

Update layout.html to support a sphinx version that is not three-integers. Useful for sphinx==5.2.0.post0, which would cause the theme to fail otherwise. Closes #1343.

Note that packaging is already a dependency transitively - but it is now an explicit dependency.

I added readthedocs-sphinx-ext as a test dependency, as I believe it is (and I couldn't get the tests passing locally without it).

[pelson]

By the way: I tested this with a theme that extends sphinx_rtd_theme, and it all checks out nicely - I am able to access sphinx_version_info from a custom layout, such as:

{% extends "sphinx_rtd_theme/layout.html" %}

{%- block htmltitle %}
{{ super() }}
Hello world
{{ sphinx_version_info  }}
{% endblock %}

Where the theme I created had a config like:

[theme]
inherit = sphinx_rtd_theme

And registering the theme with:

def config_inited_handler(app: Sphinx, config: Config) -> None:
    """
    Handler to register the theme's extra templates directory once the config
    has been read.

    """
    _ = app  # Unused.

    config.templates_path.append(str(HERE/'templates'))


def setup(app: Sphinx):
    """
    Configure the given Sphinx app to know about the acc_py theme.

    """
    app.add_html_theme('my-theme', str(HERE))
    # Register the theme's extra templates directory once the config has been
    # read.
    app.connect('config-inited', config_inited_handler)

Posting here to validate that adding the new use of app.connect("html-page-context", extend_html_context) shouldn't result in any unexpected surprises...

[benjaoming]

Posting here to validate that adding the new use of app.connect("html-page-context", extend_html_context) shouldn't result in any unexpected surprises...

This was also the one that caught my interest. But I think that it's safe. As this event is only relevant for the HTML builder, I believe that we can trust the output from the PR build.

[benjaoming]

Thanks so much @pelson for the solid work and addressing all the feedback :100: