Refactor project loading for testability. Change-Id: Ib0be12b67b2f32c809610248013b8610f234d2b7 Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/qg/+/125530 Reviewed-by: Alexei Frolov <frolv@google.com> Commit-Queue: Erik Gilling <konkers@google.com>