Refactor to make :http_frames_lib build with --config=android_arm.

cl/352042819 breaks //third_party/quic/core:quic_core_android_build target built
with --config=android_arm, because it adds :http_encoder_lib and
:http_frames_lib as dependencies of :quic_session_lib.  However,
:http_frames_lib indirectly depends on the following three targets that do not
compile with --config=android_arm:

//third_party/spdy/core:spdy_framer_lib
//third_party/quic/core/qpack:qpack_header_table_lib
//third_party/spdy/core/hpack:hpack_lib

The easiest way to fix it is this minor refactor which breaks the indirect
dependency of :http_frames_lib on these targets.

PiperOrigin-RevId: 353280950
Change-Id: Ic0f627d2d87d7e56aef1b14bc18d8f4d80e48c50

quic/core/http/http_constants.h

diff --git a/quic/core/http/http_constants.h b/quic/core/http/http_constants.h
index 37ecd20..65096a5 100644
--- a/quic/core/http/http_constants.h
+++ b/quic/core/http/http_constants.h
@@ -6,6 +6,7 @@
 #define QUICHE_QUIC_CORE_HTTP_HTTP_CONSTANTS_H_
 
 #include <cstdint>
+#include <string>
 
 #include "quic/core/quic_types.h"
 
@@ -34,6 +35,9 @@
   SETTINGS_QPACK_BLOCKED_STREAMS = 0x07,
 };
 
+// Returns HTTP/3 SETTINGS identifier as a string.
+std::string H3SettingsToString(Http3AndQpackSettingsIdentifiers identifier);
+
 // Default maximum dynamic table capacity, communicated via
 // SETTINGS_QPACK_MAX_TABLE_CAPACITY.
 const QuicByteCount kDefaultQpackMaxDynamicTableCapacity = 64 * 1024;  // 64 KB
@@ -47,6 +51,7 @@
 const uint64_t kDefaultMaximumBlockedStreams = 100;
 
 const char kUserAgentHeaderName[] = "user-agent";
+
 }  // namespace quic
 
 #endif  // QUICHE_QUIC_CORE_HTTP_HTTP_CONSTANTS_H_