libpacman: Add some finders and filters method to pacman::Database.
libpacman: s/Database::search/Database::filter/
libpacman: More Database::find methods.
libpacman: s/_pacman_db_get_pkgfromcache/Database::find/
libpacman: Add Database::whatPackagesProvide, and an extra Database::find to implement it.
libpacman: For the sake of simplicity invert packagestrmatcher_flags and strmatcher_flags in Database::find methods.
libpacman: Merge Database::find fast path to the generic api.
libpacman: s/_pacman_db_whatprovides/Database::whatPackagesProvide/
libpacman: Make Database::find(const FMatcher *packagestrmatcher) able to find regular find before provide ones.