pw_kvs: FlashPartition add erased_memory_content()

Add a erased_memory_content() getter to the FlashPartition.

Change-Id: I48a256c0d3908b7303fdc0442bcd6a63e2cc8319
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/18680
Reviewed-by: Wyatt Hepler <hepler@google.com>
Commit-Queue: David Rogers <davidrogers@google.com>
diff --git a/pw_kvs/public/pw_kvs/flash_memory.h b/pw_kvs/public/pw_kvs/flash_memory.h
index 83341ed..a486889 100644
--- a/pw_kvs/public/pw_kvs/flash_memory.h
+++ b/pw_kvs/public/pw_kvs/flash_memory.h
@@ -292,6 +292,10 @@
     return permission_ == PartitionPermission::kReadAndWrite;
   }
 
+  constexpr std::byte erased_memory_content() const {
+    return flash_.erased_memory_content();
+  }
+
   uint32_t start_sector_index() const { return start_sector_index_; }
 
  protected: