feat(core): support an offline mode build - Hash Router solution

[slorber]

Motivation

WIP/POC attempt to solve #3825 and make a Docusaurus build usable without a server, distributed as a docs.zip file for example.

This attempt assumes we want to generate a single static index.html file, and use a hash router + client-side React to render the correct page:

• index.html/#
• index.html/#/docs
• index.html/#/docs/typescript-support

See possible solutions/alternatives here:
#3825 (comment)

It seems to be a reasonable approach, although we lose the ability to emit multiple static files (which is probably not a big deal?)

Test Plan

???

Test links

• Home https://deploy-preview-9859--docusaurus-2.netlify.app/
• Doc: https://deploy-preview-9859--docusaurus-2.netlify.app/#/docs/markdown-features/tabs/
• Doc heading: https://deploy-preview-9859--docusaurus-2.netlify.app/#/docs/markdown-features/tabs/#query-string
• Doc heading + search: https://deploy-preview-9859--docusaurus-2.netlify.app/#/docs/markdown-features/tabs/?current-os=ios#query-string
• Blog: https://deploy-preview-9859--docusaurus-2.netlify.app/#/blog/releases/3.1/
• Blog heading: https://deploy-preview-9859--docusaurus-2.netlify.app/#/blog/releases/3.1/#parsefrontmatter-hook

[netlify]

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[github-actions]

⚡️ Lighthouse report for the deploy preview of this PR

URL	Performance	Accessibility	Best Practices	SEO	PWA	Report
/	🟠 75	🟢 98	🟢 96	🟢 100	🟠 88	Report
/docs/installation	🟠 68	🟢 96	🟢 100	🟢 100	🟠 88	Report
/docs/category/getting-started	🟠 75	🟢 100	🟢 100	🟢 90	🟠 88	Report
/blog	🟠 70	🟢 100	🟢 100	🟢 90	🟠 88	Report
/blog/preparing-your-site-for-docusaurus-v3	🟠 63	🟢 96	🟢 100	🟢 100	🟠 88	Report
/blog/tags/release	🟠 71	🟢 100	🟢 100	🟠 80	🟠 88	Report
/blog/tags	🟠 73	🟢 100	🟢 100	🟢 90	🟠 88	Report

[github-actions]

Size Change: -34.2 kB (-3%)

Total Size: 958 kB

Filename	Size	Change
website/build/assets/js/main.********.js	765 kB	+238 B (0%)
website/build/index.html	3.47 kB	-34.5 kB (-91%)	🏆

ℹ️ View Unchanged

Filename	Size
website/.docusaurus/globalData.json	75.4 kB
website/build/assets/css/styles.********.css	114 kB

_{compressed-size-action}

[zayne-wang]

Looking forward that this will be release in the future！

[lebalz]

What is the state of this? Is there anything we could help with to get this merged?

[slorber]

Busy on other things.

I'll try to get this merged for the next minor/major.

The POC is working but I'm not sure it's super robust regarding edge cases.

Maybe we could ship it as experimental first, and get early adopter feedback to fix bugs.