FTL: Add mixins for type-safe wrappers

For now, allow mixing in construction, default construction, equality,
ordering, incrementing, and addition.

Bug: 185536303
Test: ftl_test
Change-Id: I9017e124656ba0e7f13f378814c5b1c19a36655b
diff --git a/libs/ftl/Android.bp b/libs/ftl/Android.bp
index df0b271..8e57152 100644
--- a/libs/ftl/Android.bp
+++ b/libs/ftl/Android.bp
@@ -22,6 +22,7 @@
         "flags_test.cpp",
         "future_test.cpp",
         "match_test.cpp",
+        "mixins_test.cpp",
         "non_null_test.cpp",
         "optional_test.cpp",
         "shared_mutex_test.cpp",