Instead of mixing the source bundling with the build we make
it a separate step at the end, with cache support just like the
other stages.
Being at the end means we can reuse the cached stages from the
build if we enable bundle-sources after an existing build.
Also, this changes how the json and local files/patches are stored.
Now they are in a subdirectory called "manifest" in the sources
directory, with proper handling of relative pathnames for included
modules, etc. This also means we don't look for these file in the
extra-sources directory, but rather next to the json like we
do normally.
This adds a step to the build process to bundle
the module sources, used for building the flatpak,
as a runtime extension.
The sources can then be installed like the
debug or translation runtime.
This also adds an option to flatpak-builder
for specifying sources directories. One can specify
source dirctories with the use-sources argument. This
will skip the download part of the processing
and will extract the sources from the given sources
directory directly for further processing.
Those source directories do need the same
structure as the ones that flatpak-builder
creates during processing in .flatpak-builder
and which is also used in the exported sources
runtime.
This way you can e.g. do network i/o in them.
Thats not a recommended way to do it though, as you work around
a lot of the feature in flatpak-builder like the caching and
verification.
