Update to rtd theme v1.2.0

[Sparticuz]

This PR brings RTD up to v1.1.1. 1.2.0

Many of the upstream commits are for packaging and are not releated to mkdocs.

Here is relevant notes from their changelog:

Features

• Nicer styles for Nicer styles for <kbd> readthedocs/sphinx_rtd_theme#967
• New styling for breadcrumbs Update Breadcrumb Styles readthedocs/sphinx_rtd_theme#1073

Fixes

• Table cells with multiple paragraphs gets wrong formatting Fixes #289: Inconsistent table typography sizing readthedocs/sphinx_rtd_theme#1215
• Definition lists rendered wrongly in api docs Fix definition lists inside api docs readthedocs/sphinx_rtd_theme#1084
• Citation not styled properly Fix #1078: Citation not styled properly readthedocs/sphinx_rtd_theme#1080
• Long URLs did not wrap CSS: Add overflow-wrap to links inside paragraphs readthedocs/sphinx_rtd_theme#1193
• Fix wrapping bug on cross references Do not overflow object cross references readthedocs/sphinx_rtd_theme#1369

See #3058 (comment) for changes from 1.1.1 -> 1.2.0

Upstream compare
readthedocs/sphinx_rtd_theme@1.0.0...1.2.0

[Sparticuz]

Updating to RTD 1.2.0

• Added aria-label to search box input field. readthedocs/sphinx_rtd_theme#1380
• Added hidden text for home link in the breadcrumbs. readthedocs/sphinx_rtd_theme#1384
• Add docutils 0.18 citation/footnote support using CSS grid readthedocs/sphinx_rtd_theme#1381

@ultrabug very minor updates, two additions of an aria-label, and one css change

[oprypin]

Thanks much!