Add tippy.js support into the theme

[svekars]

Adds support for glossary tooltips in the PyTorch Sphinx Theme using the sphinx-tippy extension.

• Added a new docs/glossary.md file containing definitions for common PyTorch terms for testing.
• Created docs/test-glossary.md for testing.
• Updated docs/index.rst to include a reference to the glossary in the indices and tables section for testing
• Enabled the sphinx_tippy extension and added configuration for tooltip appearance and interactivity in docs/conf.py, along with intersphinx_mapping for external documentation references.
• Implemented a setup_tippy_defaults function in pytorch_sphinx_theme2/__init__.py to set sensible default tooltip behaviors, such as anchor selection and skip rules, and registered it with the Sphinx app.
• Added extensive SCSS for .tippy-box to ensure tooltips match the PyData Sphinx Theme’s light/dark modes, with custom styles for links, code, lists, and glossary formatting
• Compiled the theme.css with npx grunt docs
• For now, {term} links in the glossary itself won't work but if this gets merged, they will: Add tippy_glossary_base_url to fix broken glossary term links in tooltips sphinx-extensions2/sphinx-tippy#33.