Add widget_title filter to Links Widget

[ragulka]

Currently the Links Widget is the only default widget that doesn't support the widget_title filter. This is inconsistent and creates problems when plugin or theme authors want to filter widget titles - every other widget's title get's filtered, but not the Links WIdget.

Right now, displaying widget title is basically delegated to the wp_list_bookmarks function.
While this works, I suggest that this should be changed to be more consistent with other widgets - displaying widget title should really be the widget class job, not wp_list_bookmarks.

It should work with the existing wp_list_bookmarks function by specifying the categorize argument to be false.

[ocean90]

The WP_Widget_Links widget is hidden for new installs since [21501].

[SergeyBiryukov]

A lot of installs still have that widget, however fixing this inconsistency doesn't seem feasible.

Replying to ragulka:

It should work with the existing wp_list_bookmarks function by specifying the categorize argument to be false.

When there are several link categories, this would change the output of the widget from multiple lists with different titles to a single list with one title.

So it looks like link_category and wp_list_bookmarks filters are the only options here:
tags/3.8.1/src/wp-includes/bookmark-template.php#L231​.