pw_span: Move span.h to span_common.h to prep for pw::span

In the next commit, pw::span and std::span will share the span
implementation in pw_span/public/pw_span/internal/span_common.inc. To
properly track the history of the span.h file and to avoid a large diff
when all of the code moves from span.h to span_common.inc, move the file
to its new name in this CL. span.h will be re-added in the next commit
as a new file.

Change-Id: Id7290fea22029106361e0ceb5ea98bb8d51b2bef
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/98320
Reviewed-by: Ted Pudlik <tpudlik@google.com>
Commit-Queue: Wyatt Hepler <hepler@google.com>
Pigweed-Auto-Submit: Wyatt Hepler <hepler@google.com>
diff --git a/pw_protobuf/encoder.cc b/pw_protobuf/encoder.cc
index 15d6f6b..38051e7 100644
--- a/pw_protobuf/encoder.cc
+++ b/pw_protobuf/encoder.cc
@@ -26,7 +26,6 @@
 #include "pw_protobuf/serialized_size.h"
 #include "pw_protobuf/stream_decoder.h"
 #include "pw_protobuf/wire_format.h"
-#include "pw_span/internal/span.h"
 #include "pw_status/status.h"
 #include "pw_status/try.h"
 #include "pw_stream/memory_stream.h"
diff --git a/pw_span/BUILD.bazel b/pw_span/BUILD.bazel
index 94919c0..296a995 100644
--- a/pw_span/BUILD.bazel
+++ b/pw_span/BUILD.bazel
@@ -24,7 +24,7 @@
 
 pw_cc_library(
     name = "pw_span",
-    srcs = ["public/pw_span/internal/span.h"],
+    srcs = ["public/pw_span/internal/span_common.inc"],
     hdrs = ["public_overrides/span"],
     includes = [
         "public",
diff --git a/pw_span/BUILD.gn b/pw_span/BUILD.gn
index 20f525c..86c769a 100644
--- a/pw_span/BUILD.gn
+++ b/pw_span/BUILD.gn
@@ -54,7 +54,7 @@
       "$dir_pw_polyfill:iterator",
     ]
   }
-  sources = [ "public/pw_span/internal/span.h" ]
+  sources = [ "public/pw_span/internal/span_common.inc" ]
   visibility = [ ":*" ]
 }
 
diff --git a/pw_span/public/pw_span/internal/span.h b/pw_span/public/pw_span/internal/span_common.inc
similarity index 100%
rename from pw_span/public/pw_span/internal/span.h
rename to pw_span/public/pw_span/internal/span_common.inc
diff --git a/pw_span/public_overrides/span b/pw_span/public_overrides/span
index 1ac4288..c22a188 100644
--- a/pw_span/public_overrides/span
+++ b/pw_span/public_overrides/span
@@ -17,4 +17,4 @@
 #include_next <span>
 #endif  // __has_include_next(<span>)
 
-#include "pw_span/internal/span.h"
+#include "pw_span/internal/span_common.inc"