Previously rescanLibraries() was automatically called internally in
setLibrariesFolder(). This lead to double calls to rescanLibraries()
when setLibrariesFolder() was used in combination with an explicit
call to rescanLibraries().
This commit adds a new method setLibrariesFoldersAndRescan(..) and
removes the internal call to rescanLibraries() from setLibrariesFolder().
The existing setLibrariesFolder()+rescanLibraries() combos have been
replaced with setLibrariesFoldersAndRescan().
Fix#10228