pw_span: Switch from pw::span to std::span

Replace pw::span with std::span and "pw_span/span.h" with <span>
throughout the codebase.

Change-Id: Ib1fa873168b6093794e861611d750fcad6285d6c
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/12801
Commit-Queue: Wyatt Hepler <hepler@google.com>
Reviewed-by: Rob Mohr <mohrr@google.com>
Reviewed-by: Keir Mierle <keir@google.com>
diff --git a/pw_kvs/entry_cache.cc b/pw_kvs/entry_cache.cc
index 599ae80..116f27f 100644
--- a/pw_kvs/entry_cache.cc
+++ b/pw_kvs/entry_cache.cc
@@ -44,7 +44,7 @@
 
       // Remove the back entry of the address list.
       addresses_.back() = kNoAddress;
-      addresses_ = span(addresses_.begin(), addresses_.size() - 1);
+      addresses_ = std::span(addresses_.begin(), addresses_.size() - 1);
       break;
     }
   }
@@ -123,7 +123,7 @@
   // TODO(hepler): DCHECK(!full());
   Address* first_address = ResetAddresses(descriptors_.size(), entry_address);
   descriptors_.push_back(descriptor);
-  return EntryMetadata(descriptors_.back(), span(first_address, 1));
+  return EntryMetadata(descriptors_.back(), std::span(first_address, 1));
 }
 
 // TODO: This method is the trigger of the O(valid_entries * all_entries) time
@@ -214,7 +214,8 @@
   }
 }
 
-span<EntryCache::Address> EntryCache::addresses(size_t descriptor_index) const {
+std::span<EntryCache::Address> EntryCache::addresses(
+    size_t descriptor_index) const {
   Address* const addresses = first_address(descriptor_index);
 
   size_t size = 0;
@@ -222,7 +223,7 @@
     size += 1;
   }
 
-  return span(addresses, size);
+  return std::span(addresses, size);
 }
 
 EntryCache::Address* EntryCache::ResetAddresses(size_t descriptor_index,