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

android/variable.go

@@ -321,6 +321,7 @@ type productVariables struct {
 	VendorSnapshotDirsExcluded   []string `json:",omitempty"`
 	RecoverySnapshotDirsExcluded []string `json:",omitempty"`
 	RecoverySnapshotDirsIncluded []string `json:",omitempty"`
+	HostFakeSnapshotEnabled      bool     `json:",omitempty"`
 
 	BoardVendorSepolicyDirs      []string `json:",omitempty"`
 	BoardOdmSepolicyDirs         []string `json:",omitempty"`