[e.cash] Build page custom select with anchor links

Summary:
The select input on the /build page quickstart section had inconsistent styling for the dropdown box. Some browsers were getting white text on a white background.

Direct CSS styling is very inconsistent in overriding the browser styles so implementing a custom select component to maintain the same look across devices.

Also adding some logic to make anchor links work with the quickstart nav, so going to /build#examples for example will scroll to the quickstart section and have the examples tab selected. This requested feature will make it possible to link to specific quickstart sections

after

before

Test Plan: preview and test quickstart nav and anchor links

Reviewers: #bitcoin_abc, bytesofman

Reviewed By: #bitcoin_abc, bytesofman

Subscribers: bytesofman

Differential Revision: https://reviews.bitcoinabc.org/D18570