Remove all dependencies from non-test code in go/ssa to go/loader,
except the deprecated Create function which will be eliminated in
favor of ssautil.CreateProgram in a mechnanical followup.
Add Examples of two main use cases of SSA construction:
loading a complete program from source; and
building a single package, loading its dependencies from import data.
Add tests to ssautil of the two load functions.
Suggestions welcome for better names.
Planned follow-ups:
- replace all references to ssa.Create with ssautil.CreateProgram and eliminate it.
- eliminate support in go/loader for the ImportBinary flag, and the
PackageCreated hook which is no longer needed since clients can
create the package themselves (see Example).
Step 1 to fixing issue 9955.
Change-Id: I4e64df67fcd5b7f0c0388047e06cea247fddfec5
Reviewed-on: https://go-review.googlesource.com/8669
Reviewed-by: Robert Griesemer <gri@golang.org>
20186168d5