Introduce PackagingBase

PackagingBase is the base struct that implements the basic packaging
functionalities. Here, packaging means grouping dependencies into an
output file where the built artifacts from the dependencies are placed
in a directory-like structure in the output file. The exact format of
the output file is irrelevant; it could be a filesystem image, tar.gz,
zip, or whatever.

PackagingBase is responsible for traversing the dependencies and copying
their outputs under the package root directory, which is expected to be
provided by the module type that includes PackagingBase. Then the
concrete module type is expected to do final step of converting the
package root directory into the output file of specific format.

Bug: 159685774
Bug: 172414391
Test: m dist out/dist/cvd-host_package.tar.gz
Change-Id: I5446eee4834ce3b6f0f5843d93bb330a26d42fe3