Improve word-breaking of module names and sizing of main page titles

[DavidOliver]

Fixes #2189

Note: this modifies templates, so please check. Thanks.

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Adds a template function to add <wbr> after fullstops in module name titles, and uses it:

• twice in the HTML templates (module name on the API reference page in addition to the module page title);
• once in the EPUB templates.

The ebook reader I've tested with successfully breaks words on <wbr>.

Copying a module name from these headings into a text editor is still working normally for me.

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Also provides smaller main heading font sizes which apply when the content container is <= 600px in width.

Before and after:

[github-actions]

📦 Docs artifacts are ready: https://github.com/elixir-lang/ex_doc/actions/runs/21315262169/artifacts/5243794161

[josevalim]

Beautiful. I will merge and push a bit more of tests. :)

[josevalim]

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