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

snapshot/Android.bp

@@ -11,12 +11,20 @@ bootstrap_go_package {
         "soong",
         "soong-android",
     ],
+    // Source file name convention is to include _snapshot as a
+    // file suffix for files that are generating snapshots.
     srcs: [
+        "host_fake_snapshot.go",
+        "host_snapshot.go",
         "recovery_snapshot.go",
         "snapshot.go",
         "snapshot_base.go",
         "util.go",
         "vendor_snapshot.go",
     ],
+    testSrcs: [
+        "host_test.go",
+        "test.go",
+    ],
     pluginFor: ["soong_build"],
 }