Add SOONG_SDK_SNAPSHOT_VERSION support

SOONG_SDK_SNAPSHOT_VERSION=current will generate unversioned and
versioned prebuilts and a versioned snapshot module. This is the
default behavior. The zip file containing the generated snapshot will
be <sdk name>-current.zip.

SOONG_SDK_SNAPSHOT_VERSION=unversioned will generate unversioned
prebuilts only and the zip file containing the generated snapshot will
be <sdk name>.zip.

SOONG_SDK_SNAPSHOT_VERSION=<number> will generate versioned prebuilts
and a versioned snapshot module only. The zip file containing the
generated snapshot will be <sdk name>-<number>.zip.

Bug: 157884619
Test: m nothing
      m SOONG_SDK_SNAPSHOT_VERSION=current art-module-sdk
      - check that the generated Android.bp file has not changed
        from the default.
      m SOONG_SDK_SNAPSHOT_VERSION=none art-module-sdk
      - check that the generated Android.bp file does not contain
        versioned modules.
      m SOONG_SDK_SNAPSHOT_VERSION=2 art-module-sdk
      - check that the generated Android.bp file only contains
        version 2 of each module.
Change-Id: I087e9d7d3ad110508a3d6a39bca50cbb46b3ce82
diff --git a/sdk/testing.go b/sdk/testing.go
index f4e85c0..3254cf9 100644
--- a/sdk/testing.go
+++ b/sdk/testing.go
@@ -131,6 +131,7 @@
 	info := &snapshotBuildInfo{
 		t:                            t,
 		r:                            result,
+		version:                      sdk.builderForTests.version,
 		androidBpContents:            sdk.GetAndroidBpContentsForTests(),
 		androidUnversionedBpContents: sdk.GetUnversionedAndroidBpContentsForTests(),
 		androidVersionedBpContents:   sdk.GetVersionedAndroidBpContentsForTests(),
@@ -236,8 +237,13 @@
 	if dir != "" {
 		dir = filepath.Clean(dir) + "/"
 	}
-	android.AssertStringEquals(t, "Snapshot zip file in wrong place",
-		fmt.Sprintf(".intermediates/%s%s/%s/%s-current.zip", dir, name, variant, name), actual)
+	suffix := ""
+	if snapshotBuildInfo.version != soongSdkSnapshotVersionUnversioned {
+		suffix = "-" + snapshotBuildInfo.version
+	}
+
+	expectedZipPath := fmt.Sprintf(".intermediates/%s%s/%s/%s%s.zip", dir, name, variant, name, suffix)
+	android.AssertStringEquals(t, "Snapshot zip file in wrong place", expectedZipPath, actual)
 
 	// Populate a mock filesystem with the files that would have been copied by
 	// the rules.
@@ -432,6 +438,11 @@
 	// The result from RunTest()
 	r *android.TestResult
 
+	// The version of the generated snapshot.
+	//
+	// See snapshotBuilder.version for more information about this field.
+	version string
+
 	// The contents of the generated Android.bp file
 	androidBpContents string