Support Article Dialog: add support to scroll to anchor and refactor to functional component

[gwwar]

This PR updates the Support Article Dialog to a functional component and also adds support to scroll to an anchor point if specified in the postUrl.

So for example:

Without Anchor	Support Page with Anchor

Testing Instructions

• Spin up the branch
• In console dispatch( { type: 'SUPPORT_ARTICLE_DIALOG_OPEN', postId: 145498, postUrl: 'https://support.wordpress.com/free-photo-library/' } ) opens the support dialog to the top of the page content.
• In console dispatch( { type: 'SUPPORT_ARTICLE_DIALOG_OPEN', postId: 145498, postUrl: 'https://support.wordpress.com/free-photo-library/#add-images-from-a-post-or-page' } ) scrolls to the correct anchor point
• In console dispatch( { type: 'SUPPORT_ARTICLE_DIALOG_OPEN', postId: 147594, postUrl: 'https://wordpress.com/support/wordpress-editor/#blocks' } ) scrolls to the correct anchor point
• In console dispatch( { type: 'SUPPORT_ARTICLE_DIALOG_OPEN', postId: 147594, postUrl: 'https://wordpress.com/support/wordpress-editor/#configuring-a-block' } ) scrolls to the correct anchor point
• No regressions with existing inline help (?) or the free photo library card in My Home

[matticbot]

Test live: https://calypso.live/?branch=add/support-anchor-link

[gwwar]

@mmtr feel free to land this for me if changes look good 👍

[mmtr]

Nice work @gwwar!

[matticbot]

Here is how your PR affects size of JS and CSS bundles shipped to the user's browser:

Async-loaded Components (~24 bytes added 📈 [gzipped])

name                                             parsed_size           gzip_size
async-load-blocks-support-article-dialog-dialog       -212 B  (-0.3%)      +24 B  (+0.1%)

React components that are loaded lazily, when a certain part of UI is displayed for the first time.

Legend

What is parsed and gzip size?

Parsed Size: Uncompressed size of the JS and CSS files. This much code needs to be parsed and stored in memory.
Gzip Size: Compressed size of the JS and CSS files. This much data needs to be downloaded over network.

Generated by performance advisor bot at iscalypsofastyet.com.

[mmtr]

Tests are quite flakey in all PRs. I'm not being able to get a clean build, so I'm going to land this in order to unblock #39617 (double checked in p1586431438072700-slack-e2e-testing-discuss @Automattic/e2e-test-reviewers are aware of the Timed out waiting for element with css selector of '#loginAsAnotherUser' to be clickable errors and are working on them, so this should be safe to land in the meantime).