get_term() is missing cache in some cases

[boonebgorges]

As reported in ​https://wordpress.org/support/topic/tagcloud-widget-categories-significant-sql-query-increase?replies=2. On sites with large numbers of categories, both tag cloud and category widgets are missing the cache when building markup (via get_term_link() -> get_term()). My bisect tools are telling me that this dates from [29915]; see #21760. The changes related to #21760 were supposed to have been reverted in [30900], but it appears that something was missed there. I'm investigating.

[boonebgorges]

30749.patch​ fixes the issue. As I suspected, I missed something when cleaning up #21760 [30900] - get_terms() must update the cache for the term objects that it locates. I've added a unit test to make sure this doesn't happen again.

[boonebgorges]

30749.2.patch​ adds unit tests for the other cache-setting parts that were touched in [30900]. Everything is passing as expected.

[boonebgorges]

In 30954:

Update individual term caches in get_terms().

This was removed in [29915] as part of the attempt to add cache support to
get_term_by(). When that support was removed in [30900], it was not properly
restored.

This changeset includes a unit test to verify that the cache is properly primed
for terms found in get_terms(), as well as tests to verify the other cache
setting that was touched by [30900].

Fixes #30749. See #21760.

[boonebgorges]

Reopening for the 4.1 branch.

[nacin]

In 30959:

Update individual term caches in get_terms().

Merges [30954] to the 4.1 branch.

props boonebgorges.
fixes #30749. see #21760.