pw_kvs: Use pw::Vector for descriptor lists

The pw::Vector class is similar to std::vector but is backed by a
fixed-size array. Using pw::Vector for descriptor lists cleans up the
code and makes iterating over these lists less error-prone. It also
opens the possibility of working with descriptor types that are not
default constructible.

Change-Id: I3ad05dacef1cc77108a9d35128aa2100535048b2
diff --git a/pw_kvs/BUILD b/pw_kvs/BUILD
index 522325c..b5db383 100644
--- a/pw_kvs/BUILD
+++ b/pw_kvs/BUILD
@@ -41,6 +41,7 @@
     includes = ["public"],
     deps = [
         "//pw_checksum",
+        "//pw_containers",
         "//pw_log",
         "//pw_status",
     ],