feat(docs): add search capability

[lucivpav]

This PR adds a search input to the top part of sidebar. The search goes through all the below tree's sections, effectively filtering those that match the query. The items are matched in case-insensitive fashion.

As you can see, the icon is not rendered at an expected position. This looks like a bug in Input component, reported here.

The search input is not fully accessible - it does not let the user know, how many items were found (matching the query). This would be solved in a future PR.

You can search by typing even when the element is not focused (provided no other input element is in focus).

[codecov]

Codecov Report

Merging #1682 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1682   +/-   ##
=======================================
  Coverage   71.06%   71.06%           
=======================================
  Files         862      862           
  Lines        7172     7172           
  Branches     2082     2082           
=======================================
  Hits         5097     5097           
  Misses       2069     2069           
  Partials        6        6

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 5a49f1f...405cdd5. Read the comment docs.

[lucivpav]

Problem: category of currently selected section cannot be collapsed anymore.

[lucivpav]

Problem: category of currently selected section cannot be collapsed anymore.

Fixed.

[lucivpav]

Icon's location has been fixed by manually setting the icon's padding.

[mnajdova]

I would expect that Concepts, Guides and Prototypes would not be visible in this case