Move third_party/base/span.h to core/fxcrt

Fix some GN build rules to make the build work after moving.

Bug: pdfium:2127
Change-Id: Ic8cf0860dc5df8a510ecb34de1ffd10514d86c26
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/116650
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Reviewed-by: Thomas Sepez <tsepez@google.com>
Commit-Queue: Lei Zhang <thestig@chromium.org>
diff --git a/testing/fuzzers/pdf_cmap_fuzzer.cc b/testing/fuzzers/pdf_cmap_fuzzer.cc
index 58dfbe6..030ffd9 100644
--- a/testing/fuzzers/pdf_cmap_fuzzer.cc
+++ b/testing/fuzzers/pdf_cmap_fuzzer.cc
@@ -6,7 +6,7 @@
 
 #include "core/fpdfapi/font/cpdf_cmap.h"
 #include "core/fxcrt/retain_ptr.h"
-#include "third_party/base/containers/span.h"
+#include "core/fxcrt/span.h"
 
 extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
   if (size > 256 * 1024)