Fix markup for table of contents on privacy policy guide

[ocean90]

There are a few issues with current ToC:

1. The Introduction link has an empty anchor. It should have a specific one just like the others: https://core.trac.wordpress.org/browser/trunk/src/wp-admin/includes/misc.php?rev=43242&marks=1606#L1606
2. Instead of the empty anchor tag the ID can be directly assigned to the headline: https://core.trac.wordpress.org/browser/trunk/src/wp-admin/includes/misc.php?rev=43242&marks=1636#L1636
3. The date format should be consistent across the admin, see [35811]. get_option( 'date_format' ) needs to be replaced: https://core.trac.wordpress.org/browser/trunk/src/wp-admin/includes/misc.php?rev=43242&marks=1607#L1607
4. The ToC IDs are not guaranteed to be unique on the page. I suggest to prefix them with policy-<plugin name> or something else: https://core.trac.wordpress.org/browser/trunk/src/wp-admin/includes/misc.php?rev=43242&marks=1632#L1632

[azaozz]

In 44056.patch:

• Add ID to the "Introduction" heading and use it to scroll to it.
• Add translatable date format instead of user selected one.
• Add prefix to HTML IDs used for the ToC.

We can't add IDs to the headings as they are "too low". Unfortunately the browsers scroll-into-view is still somewhat buggy and doersn't take into account HTML elements that may cover the top. If we add the IDs to the headings or use empty anchors, the actual headings are scrolled under the admin toolbar. Tested in FF, Chrome, Edge and IE11, all do that :(

[ocean90]

Let's go with 44056.2.patch​ for now.

As mentioned on Slack, I tried the :target way but then I remembered that it requires a huge gap between the sections otherwise you wouldn't be able to click the Copy button anymore due to the negativ top margin.

[azaozz]

In 43265:

Privacy: fix markup for the table of contents on privacy policy guide screen.

Props ocean90, azaozz.
Fixes #44056.

[azaozz]

In 43266:

Privacy: fix markup for the table of contents on privacy policy guide screen.

Props ocean90, azaozz.
Merges [43265] to the 4.9 branch.
Fixes #44056.

[desrosj]

Moving to the new Privacy component.