Rewrite styleguide-search to vanilla JS

[Wolfr]

Rewrite styleguide-search (https://github.com/usebedrock/bedrock/blob/develop/core/js/styleguide-search.js) to vanilla JS.

Should be fairly simple, 27 lines of code. Some notes:

• $(this).parent() --> parentNode
• $('#styleguideSearch') --> document.getElementById(styleguideSearch);
• Show and hide can be done by setting style.display

[Wolfr]

This was implemented in d9ff27c

[Wolfr]

The code that was PR'd has its problems, one of which is still using parts of jQuery.

I implemented a standalone filter as a codepen, we can use this type of code to implement it in Bedrock.

https://codepen.io/wolfr/pen/GRvPRry