Support storing SHA256 checksum for files in soong_zip

Add a -sha256 argument to soong_zip that computes SHA256 checksum for
each file and stores the value in file header. The SHA information can
then be used by downstream systems that use content addressing.

Bug: 259513199
Test: zip_test.go
Test: soong_zip -o test.zip -D test_dir -sha256
Change-Id: I20e9f424bd0a4604f0dc7cc77bd65f10eb49a163

zip/cmd/main.go

@@ -163,6 +163,7 @@ func main() {
 	parallelJobs := flags.Int("parallel", runtime.NumCPU(), "number of parallel threads to use")
 	cpuProfile := flags.String("cpuprofile", "", "write cpu profile to file")
 	traceFile := flags.String("trace", "", "write trace to file")
+	sha256Checksum := flags.Bool("sha256", false, "add a zip header to each file containing its SHA256 digest")
 
 	flags.Var(&rootPrefix{}, "P", "path prefix within the zip at which to place files")
 	flags.Var(&listFiles{}, "l", "file containing list of files to zip")
@@ -224,6 +225,7 @@ func main() {
 		WriteIfChanged:           *writeIfChanged,
 		StoreSymlinks:            *symlinks,
 		IgnoreMissingFiles:       *ignoreMissingFiles,
+		Sha256Checksum:           *sha256Checksum,
 	})
 	if err != nil {
 		fmt.Fprintln(os.Stderr, "error:", err.Error())