Add module based host-tools snapshot

Add new module:
host_snapshot {
    name: "host-snapshot"
    deps: [
      (list of host tools)
    ],
    ...
}

Package host tools using android.PackagingBase to capture host tools and transitive packaging data.
Add JSON meta data to snapshot that allows snapshot to be installed via development/vendor_snapshot/update.py

Add support to generate a fake host snapshot of all host modules that is used to detect required
modules via development/vendor_snapshot/update.py.

Bug: 192556798
Bug: 194799048
Bug: 192896149
Test: m HOST_FAKE_SNAPSHOT_ENABLE=true host-fake-snapshot dist -- check snapshot exists in dist

Change-Id: I849c4db801cd858408f6fe6a3ce69262a23a5be9
diff --git a/snapshot/snapshot_base.go b/snapshot/snapshot_base.go
index de93f3e..79d3cf6 100644
--- a/snapshot/snapshot_base.go
+++ b/snapshot/snapshot_base.go
@@ -102,3 +102,19 @@
 		return isDirectoryExcluded(filepath.Dir(dir), excludedMap, includedMap)
 	}
 }
+
+// This is to be saved as .json files, which is for development/vendor_snapshot/update.py.
+// These flags become Android.bp snapshot module properties.
+//
+// Attributes are optional and will be populated based on each module's need.
+// Common attributes are defined here, languages may extend this struct to add
+// additional attributes.
+type SnapshotJsonFlags struct {
+	ModuleName          string `json:",omitempty"`
+	RelativeInstallPath string `json:",omitempty"`
+	Filename            string `json:",omitempty"`
+	ModuleStemName      string `json:",omitempty"`
+
+	// dependencies
+	Required []string `json:",omitempty"`
+}