fix(theme): preserve url ?search#hash on navbar version/locale dropdowns navigations

[slorber]

Motivation

?search#hash shouldn't be lost when switchiung version or locale through the navbar dropdowns.

A querystring/hash may be used to enable some page-specific behavior that we want to preserve:

• linking to a specific heading
• integration with hash-based routing libs (see How to extend the functionality of docsVersionDropdown #8057 (reply in thread))
• opening a specific tab (see Open respective tab item with URL query string #7008)
• other behaviors

Test Plan

preview / dogfood

Test links

Deploy preview:

• https://deploy-preview-8059--docusaurus-2.netlify.app/docs/installation
• https://deploy-preview-8059--docusaurus-2.netlify.app/docs/installation?qs=true
• https://deploy-preview-8059--docusaurus-2.netlify.app/docs/installation?qs=true#build
• https://deploy-preview-8059--docusaurus-2.netlify.app/docs/installation#build
• https://deploy-preview-8059--docusaurus-2.netlify.app/docs/installation#anchor-that-does-not-exist

[netlify]

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[github-actions]

⚡️ Lighthouse report for the deploy preview of this PR

URL	Performance	Accessibility	Best Practices	SEO	PWA	Report
/	🟠 62	🟢 98	🟢 100	🟢 100	🟠 80	Report
/docs/installation	🟠 81	🟢 98	🟢 100	🟢 100	🟢 90	Report

[github-actions]

Size Change: +162 B (0%)

Total Size: 813 kB

Filename	Size	Change
website/build/assets/js/main.********.js	609 kB	+162 B (0%)

ℹ️ View Unchanged

Filename	Size
website/.docusaurus/globalData.json	52.1 kB
website/build/assets/css/styles.********.css	111 kB
website/build/index.html	40.8 kB

_{compressed-size-action}

[slorber]

when switching version on a hash that doesn't lead to any existing heading (for example a routing hash, cf examples), the navbar disappears 😅

[Josh-Cena]

Shall we fix that one before merging this? I fear that's an even weirder UX.

[slorber]

looks like there are some weird edge-cases to consider, but should be good enough for now

Example weird edge case: the dropdown not disappearing because it remains hovered, while navbar disappears

I'm not the the prod behavior of this hideable navbar is 100% good atm anyway 🤷‍♂️