Spell out inet and lwip sources in GN (#31931)

* Spell out inet and lwip sources

Prepare to have some scripts that force all headers/sources to be known to GN.

* Fix some copy and paste issues

* Another copy and paste issue fixed

* Restyle
diff --git a/src/inet/BUILD.gn b/src/inet/BUILD.gn
index 09a6e56..94d6c25 100644
--- a/src/inet/BUILD.gn
+++ b/src/inet/BUILD.gn
@@ -72,9 +72,20 @@
   deps = [ ":inet_buildconfig" ]
 }
 
+source_set("impl_header") {
+  sources = [ "InetInterfaceImpl.h" ]
+  public_configs = [ "${chip_root}/src:includes" ]
+  public_deps = [ "${chip_root}/src/system:system_config_header" ]
+}
+
 static_library("inet") {
   output_name = "libInetLayer"
 
+  # EndpointState header is one of:
+  #   - src/inet/EndPointStateLwIP.h
+  #   - src/inet/EndPointStateNetworkFramework.h
+  #   - src/inet/EndPointStateOpenThread.h
+  #   - src/inet/EndPointStateSockets.h
   sources = [
     "EndPointBasis.h",
     "EndPointState${chip_system_config_inet}.h",
@@ -98,6 +109,7 @@
   ]
 
   public_deps = [
+    ":impl_header",
     ":inet_config_header",
     "${chip_root}/src/lib/core:types",
     "${chip_root}/src/lib/support",
@@ -115,6 +127,13 @@
   }
 
   if (chip_inet_config_enable_tcp_endpoint) {
+    # Possible TCPEndpointImpl files:
+    #  - TCPEndPointImplLwIP.cpp
+    #  - TCPEndPointImplLwIP.h
+    #  - TCPEndPointImplOpenThread.cpp
+    #  - TCPEndPointImplOpenThread.h
+    #  - TCPEndPointImplSockets.cpp
+    #  - TCPEndPointImplSockets.h
     sources += [
       "TCPEndPoint.cpp",
       "TCPEndPoint.h",
@@ -125,6 +144,15 @@
   }
 
   if (chip_inet_config_enable_udp_endpoint) {
+    # Possible UDPEndpointImpl files:
+    #  - UDPEndPointImplLwIP.cpp
+    #  - UDPEndPointImplLwIP.h
+    #  - UDPEndPointImplNetworkFramework.cpp
+    #  - UDPEndPointImplNetworkFramework.h
+    #  - UDPEndPointImplOpenThread.cpp
+    #  - UDPEndPointImplOpenThread.h
+    #  - UDPEndPointImplSockets.cpp
+    #  - UDPEndPointImplSockets.h
     sources += [
       "BasicPacketFilters.h",
       "EndpointQueueFilter.h",
@@ -134,6 +162,12 @@
       "UDPEndPointImpl${chip_system_config_inet}.h",
       "UDPEndPointImpl.h",
     ]
+
+    if (chip_system_config_inet == "Sockets") {
+      # TODO: dependency on this one is not clear as it is only ever
+      #       enabled through CMakeLists.txt. Added here for completeness
+      sources += [ "ZephyrSocket.h" ]
+    }
   }
 
   if (chip_with_nlfaultinjection) {
diff --git a/src/inet/tests/TestInetLayer.h b/src/inet/tests/TestInetLayer.h
deleted file mode 100644
index 1c13b7d..0000000
--- a/src/inet/tests/TestInetLayer.h
+++ /dev/null
@@ -1,39 +0,0 @@
-/*
- *
- *    Copyright (c) 2020 Project CHIP Authors
- *
- *    Licensed under the Apache License, Version 2.0 (the "License");
- *    you may not use this file except in compliance with the License.
- *    You may obtain a copy of the License at
- *
- *        http://www.apache.org/licenses/LICENSE-2.0
- *
- *    Unless required by applicable law or agreed to in writing, software
- *    distributed under the License is distributed on an "AS IS" BASIS,
- *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- *    See the License for the specific language governing permissions and
- *    limitations under the License.
- */
-
-/**
- *    @file
- *      This file declares test entry points for CHIP Internet (inet)
- *      layer library unit tests.
- *
- */
-
-#pragma once
-
-#ifdef __cplusplus
-extern "C" {
-#endif
-
-int TestInetAddress(void);
-int TestInetBuffer(void);
-int TestInetErrorStr(void);
-int TestInetTimer(void);
-int TestInetEndPoint(void);
-int TestInetLayerDNS(void);
-#ifdef __cplusplus
-}
-#endif
diff --git a/src/platform/android/BUILD.gn b/src/platform/android/BUILD.gn
index bd9f3cd..a6e1fd6 100644
--- a/src/platform/android/BUILD.gn
+++ b/src/platform/android/BUILD.gn
@@ -84,7 +84,10 @@
 
 source_set("inet") {
   sources = [ "InetInterfaceImpl.cpp" ]
-  deps = [ "${chip_root}/src/lib/support" ]
+  deps = [
+    "${chip_root}/src/inet:impl_header",
+    "${chip_root}/src/lib/support",
+  ]
 }
 
 android_library("java") {
diff --git a/src/system/BUILD.gn b/src/system/BUILD.gn
index 5953dc6..1389bdd 100644
--- a/src/system/BUILD.gn
+++ b/src/system/BUILD.gn
@@ -248,6 +248,12 @@
   ]
 
   if (chip_system_layer_impl_config_file == "") {
+    # This includes one of:
+    #    - SystemLayerImplFreeRTOS.h
+    #    - SystemLayerImplFreeRTOS.cpp
+    # or
+    #    - SystemLayerImplSelect.h
+    #    - SystemLayerImplSelect.cpp
     sources += [
       "SystemLayerImpl${chip_system_config_event_loop}.cpp",
       "SystemLayerImpl${chip_system_config_event_loop}.h",