Added support for conversion from a standard package which contains
pointers to read only strings to fully self-contained (fsc) package.
Fsc package contains all strings associated with the package thus
access to read only strings is not needed to format a string.
In order to allow conversion to fsc package, standard package must
contain locations of all string pointers within the package. Appending
that information is optional and is controlled by flags parameter
which was added to packaging API. If option flag is set then
package contains header, arguments, locations of read only strings and
transient strings (each prefixed with string argument location).
Package header has been extended with field which contains number of
read only string locations.
A function for conversion to fsc package has been added
(cbprintf_fsc_package()).
Signed-off-by: Krzysztof Chruscinski <krzysztof.chruscinski@nordicsemi.no>