add docsearch

[maxiloc]

Following my comment in #22711, I made this PR using the snippet I gave you so you can have
a look at how it looks.

Happy to have your feedback on this.

[mdo]

Dope! Thanks for tackling this!

My only question is how can we hook this up so that it searches and navigates to the local docs when in development? I've grown quite accustomed to searching for pages when working on Bootstrap, and I imagine others might be confused when they jump to the production site. Any thoughts?

[maxiloc]

@mdo I updated the PR so the search also redirect correctly when in development mode.
Tell me if that works for you.

[mdo]

I cherry picked the commits from here and have them in #22716 now. Woot! Thanks so much @maxiloc. Let me know how I can help ensure the index stays up to date (I can add it to our shipping checklist). Also take a look at that PR—I've tweaked the design a bit and would love your input.

[maxiloc]

Hey I have just checked the new design of the search, I am having some style issues with the dropdown. Is that expected ? Happy to help on this if needed.

Regarding the updates of the index, what we can propose is to run a reindex every 30min, would that work for you ?

[mdo]

Hmm, I'm not seeing that in Chrome or Safari on my end. Do you have the latest dist files built?

[maxiloc]

I pulled again, I don't have that anymore.

[mdo]

Commits were cherry-picked into my other branch, which just merged, so we're good to go!