FTL: Add Expected<T, E>

Extend `base::expected` with `has_error()` and `value_opt()`.

Bug: 185536303
Test: ftl_test
Change-Id: I07d70dc8fe7ebfe2f08626dff51aef0b98430f61
diff --git a/libs/ftl/Android.bp b/libs/ftl/Android.bp
index 918680d..5ac965f 100644
--- a/libs/ftl/Android.bp
+++ b/libs/ftl/Android.bp
@@ -10,11 +10,15 @@
 cc_test {
     name: "ftl_test",
     test_suites: ["device-tests"],
+    header_libs: [
+        "libbase_headers",
+    ],
     srcs: [
         "algorithm_test.cpp",
         "cast_test.cpp",
         "concat_test.cpp",
         "enum_test.cpp",
+        "expected_test.cpp",
         "fake_guard_test.cpp",
         "flags_test.cpp",
         "function_test.cpp",