Add localization to package daemon and solver

Thanks to Adrien and Rene for reviewing and guidance.
Fixes #13282.

Merge branch 'package-management'

Conflicts:
src/preferences/network/Jamfile

package kit: Add data structures for problem solutions

... and add the problem solutions in LibsolvSolver.

Flesh out the package kit solver API quite a bit more

* Reorganize things a bit:
- BSolver is now an abstract base class.
- A libsolv based implementation, LibsolvSolver, lives in a new
add-

Flesh out the package kit solver API quite a bit more

* Reorganize things a bit:
- BSolver is now an abstract base class.
- A libsolv based implementation, LibsolvSolver, lives in a new
add-on, which is loaded lazily.
- Get rid of libpackage_solver. Save for LibsolvSolver everything
is moved to libpackage.
- This is a nicer solution for the cyclic dependency caused by
libsolv (libsolvext to be precise) using the package kit for
reading repositories and package files.
* Add a solver result data structure and and an accessor the solver.
* Add problem reporting support to the solver. There aren't data
structures for the problem solutions yet and support for selecting
solutions and re-solving is missing as well.

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