Make our search button show in the header on mobile

[choldgraf]

Context

Currently, our search button lives in navbar_end and behaves similarly to all of the other buttons. However, it is common for people to want to search for things moreso than clicking icon links etc, and so it is a bit annoying when you have to click 2 times in order to do that.

A pattern I've seen in a few places is to put the search button as a "sibling" of the "collapse button" when you're on mobile. That way people can click to search with one click from the mobile landing page. For example, from the Wowchemy docs:

Material for mkdocs:

Proposal

I propose that we special-case the search button so that it shows up just next to the "collapse header" button by default on mobile.

[drammock]

Agreed.

[12rambau]

LGTM

[12rambau]

it @choldgraf, isn't it now solved in main with your new interface for the header navbbar ?

[choldgraf]

Yes! Good catch. I believe this was closed by #832