Prior to the introduction of `WP_Term_Query`, the 'orderby' clause
passed to the 'terms_clauses' filter was prefixed by `ORDER BY`. After
`WP_Term_Query`, this was not the case; `ORDER BY` was added after the
filter. As such, plugins filtering 'terms_clauses' and returning an
'orderby' clause beginning with `ORDER BY` resulted in invalid syntax
when `WP_Term_Query` prepended a second `ORDER BY` keyword to
the clause.
This changeset rearranges the way the 'orderby' clause is built so that
it will be passed to 'terms_clauses' in the previous format.
Fixes#37378.
Built from https://develop.svn.wordpress.org/trunk@38099
git-svn-id: http://core.svn.wordpress.org/trunk@38040 1a063a9b-81f0-0310-95a4-ce76da25c4cd
`WP_Term_Query` is modeled on existing query classes, such as those used
for comments and users. It provides a more consistent structure for generating
term queries, and should make it easier to add new functionality in the future.
Props flixos90, boonebgorges.
See #35381.
Built from https://develop.svn.wordpress.org/trunk@37572
git-svn-id: http://core.svn.wordpress.org/trunk@37540 1a063a9b-81f0-0310-95a4-ce76da25c4cd
