Like Weston suggested, add this to the
amp_validation_error term description.
This will aid in searching that taxonomy page
by error type.
At the moment, there are only 3 types:
HTML, JS, and CSS.

For example, onclick.
This will have JS in it, so this error code is more accurate.
On Weston's suggestion in code review.

These were for an onload attribute,
so update them for the latest commit.

Borrowing heavily from:
add_group_terms_clauses_filter(),
filter the 'where' clause,
to filter the taxonomy page by type.

On clicking the 'Filter' button on the 'AMP Validation Errors' taxonomy page,
edit-tags.php processes the POST request that this submits.
Then, it redirects to a URL to display the page again.
This filter callback looks for a value for VALIDATION_ERROR_TYPE_QUERY_VAR in the  request.
That means that the user filtered by error type, like 'js_error'.
It then passes that value to the redirect URL as a query var,
So that the taxonomy page will be filtered for that error type.
@see AMP_Validation_Error_Taxonomy::add_error_type_clauses_filter() for the filtering of the 'where' clause, based on that query var.

Allows filtering by error_type,
like only viewing JS errors.
This UI now works for error_type,
though work is probably needed for accepted status.

This still doesn't use the new terminology, like 'Identified.'
There wasn't much to change,
as filtering by error type worked thanks to Weston.

Though these views are now applied in a <select> filter,
this uses much of their infrastructure.
Also, it uses their counts for each status.
For example, if there are 0 accepted errors,
this won't display the <option> for 'Accepted Error'.

Create a new constant, NO_FILTER_VALUE.
This is for the existing value of -1.
And add this to the whitelist: in_array().

Change this to 'Errors by Type,'
to match the Sketch design.

There were counts earlier,
when filtering by status was done by clicking an <a>.
Thanks to Weston's work.
Mainly copy the previous logic to add the counts.

Before, there was only HTML_ERROR_TYPE.
Based on comments in issues like 1361,
this adds 2 types of errors for HTML.

The AMP validation error page also needs these filters,
but it doesn't need all of
render_taxonomy_filters().
So abstract it into 2 functions that can be reused.

Using the functions created earlier,
output the filter <select> elements on this page.
There's more work remaining,
like ensuring the query vars work.

Mainly by using the method that Weston wrote:
filter_posts_where_for_validation_error_status()
Look for the query var of the error type.
And if that's present, add to the WHERE clause.

This is at the top of the taxonomy page (Errors by Type),
and links to the post page (Errors by URL).

Instead of an if block for most of the method,
simply return if the condition is false.
Then, the remaining if blocks aren't nested.

Before, that didn't take account of the filter for error type
So if that filtered for js_error,
the total count of error status was the same as if it
were for 'All Error Types.'
So look for the query var for the error type,
and pass that to the WP_Query if it's valid.

…rors'

This is how the text was when it was inside a link.
Check for the current screen,
and conditionally add the 'With'.

… redirect

Before, the filter for the redirect URL
did not accept -1,
which is for 'All Error Types' and 'All Statuses'.
This means that the URL sometimes did not redirect,
and it sometimes showed the same results as before.

Make PHP DocBlocks more clear,
especially when they needed to be updated.

…idation_error_status

…ion when changing selected error type