[soong] new field in Android.bp to request APK signing V4

If "v4_signature: true" is set, the v4 signature file,
named [outputApkFile].idsig
will be generated along side the outputApkFile.

Test: m nothing
Test: atest PackageManagerShellCommandIncrementalTest
BUG: 149354175
Change-Id: Ie84725a15406f96f65042ea9909460e4eb34d57f