Make the recently accessed folder list globally accessible

This is normally managed by RecentCollectionAction, but is only updated
by StandardActionManager when its standard actions are used.  If a
caller uses its own actions, for example KMail's separate message reader
window, then the list is not updated.

Add a static function StandardActionManager::addRecentCollection(),
which simply calls RecentCollectionAction::addRecentCollection() to
update the global recent collection list.  Read and update this list in
RecentCollectionAction as before.

2 jobs for !57 with recent-collection-static-access in 17 minutes and 37 seconds (queued for 1 second)
latest detached
Status Job ID Name Coverage
failed #99829


passed #99828
linux kf5-qt5 qt5.15


Name Stage Failure
build_clazy_clang_tidy Build
[ 11%] Linking CXX executable ../../bin/akonadi_control
[ 11%] Built target akonadi_control
make: *** [Makefile:160: all] Error 2
Uploading artifacts for failed job
Uploading artifacts...
WARNING: build/clang-tidy-report.xml: no matching files
ERROR: No files to upload
Cleaning up file based variables
ERROR: Job failed: exit code 1