Add a soong var that will be used to enable/disabe rust relevant targets am:...

Add a soong var that will be used to enable/disabe rust relevant targets am: 5b7787ec am: 5e6a2f7e am: 7892e66a

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/modules/DnsResolver/+/13929889

Change-Id: Ie0379acf222db694b5a7bdfaf47681d774ffe1b4