Add missing Abseil inline namespace and fix includes

PiperOrigin-RevId: 686110246
Change-Id: I78be07f1c6795d282c3739c54764b1562fd2523c

absl/strings/BUILD.bazel

@@ -392,7 +392,7 @@ cc_library(
     linkopts = ABSL_DEFAULT_LINKOPTS,
     deps = [
         ":string_view",
-        "//absl/base:core_headers",
+        "//absl/base:config",
     ],
 )
 

absl/strings/CMakeLists.txt

@@ -100,7 +100,7 @@ absl_cc_library(
   COPTS
     ${ABSL_DEFAULT_COPTS}
   DEPS
-    absl::core_headers
+    absl::config
     absl::string_view
   PUBLIC
 )

absl/strings/charset.h

@@ -46,15 +46,13 @@
 #ifndef ABSL_STRINGS_CHARSET_H_
 #define ABSL_STRINGS_CHARSET_H_
 
-#include <cstddef>
 #include <cstdint>
-#include <cstring>
 
-#include "absl/base/macros.h"
-#include "absl/base/port.h"
+#include "absl/base/config.h"
 #include "absl/strings/string_view.h"
 
 namespace absl {
+ABSL_NAMESPACE_BEGIN
 
 class CharSet {
  public:
@@ -159,6 +157,7 @@ class CharSet {
   uint64_t m_[4];
 };
 
+ABSL_NAMESPACE_END
 }  // namespace absl
 
 #endif  // ABSL_STRINGS_CHARSET_H_