Add min_sdk_version to Rust modules.

Add the min_sdk_version property to Rust modules so they can declare
a minimum SDK version they support for use with APEX modules.

Test: New Soong test passes.
Bug: 174862583
Change-Id: I2829053a320f50c218783dee5adbeff9cef81e8e
diff --git a/rust/testing.go b/rust/testing.go
index a8496d9..8648dc3 100644
--- a/rust/testing.go
+++ b/rust/testing.go
@@ -78,6 +78,7 @@
 			nocrt: true,
 			system_shared_libs: [],
 			apex_available: ["//apex_available:platform", "//apex_available:anyapex"],
+			min_sdk_version: "29",
 		}
 		cc_library {
 			name: "libprotobuf-cpp-full",
@@ -95,6 +96,7 @@
                         native_coverage: false,
 			sysroot: true,
 			apex_available: ["//apex_available:platform", "//apex_available:anyapex"],
+			min_sdk_version: "29",
 		}
 		rust_library {
 			name: "libtest",
@@ -105,6 +107,7 @@
                         native_coverage: false,
 			sysroot: true,
 			apex_available: ["//apex_available:platform", "//apex_available:anyapex"],
+			min_sdk_version: "29",
 		}
 		rust_library {
 			name: "libprotobuf",