[Places panel] Revamp the Recently Saved section

Summary:
FEATURE: 110016
FEATURE: 159299
FEATURE: 311218
FIXED-IN: 5.63

Revamp the Recently Saved section, including the following changes:

• Change the section name to "Recent"
• Change the name of the existing entries to "Modified Today" and "Modified Yesterday", for clarity.
• Add "Recent Files" and "Recent Locations" item corresponding to recentlyused:/files and recentlyused:/locations listing the last 30 files or directories accessed in the current activity, and adjust the code to support this.

Depends on D22144
Depends on D23742
Depends on D23737
Depends on D23741
Depends on D23760

Test Plan:
LANG="EN" ctest

Adds "Recent Files" "Recent Locations" entries to user accounts places recent group.

Reviewers: Dolphin, broulik, elvisangelaccio, VDG, Frameworks, ngraham

Reviewed By: Dolphin, elvisangelaccio, VDG, ngraham

Subscribers: meven, trickyricky26, andreask, huftis, svenmauch, kde-frameworks-devel, spoorun, andreaska, gregormi, markg, alexeymin, broulik, elvisangelaccio, dfaure, davidedmundson, ltoscano, Konqueror

Tags: Dolphin, Frameworks

Maniphest Tasks: T8349

Differential Revision: https://phabricator.kde.org/D7446