Move matter_enable_recommended into /config/recommended.gni

This allows it to be uesd from args.gni (i.e. in the context of a default_args
scope, where variables like current_os are not defined) as well as within a
build / toolchain context.

config/recommended.gni

@@ -0,0 +1,31 @@
+# Copyright (c) 2024 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.
+
+declare_args() {
+  # Note for SDK developers:  As additional features with their own settings
+  # are added to the SDK, consider using the `matter_enable_recommended`
+  # meta-setting instead of a default value of 'true', especially where a
+  # different default is used based on platform (current_os): Often various
+  # debugging features have previously been defaulted to on for Linux and/or
+  # Mac but off for embedded platforms (on the assumption that Linux / Mac
+  # don't have resource constraints?); build settings of that nature should
+  # instead reference this meta-setting. E.g.
+  #   enable_flux_capacitor =  matter_enable_recommended && current_os == "linux"
+
+  # Enable recommended settings by default. This is a meta-setting
+  # that is enabled by default, and acts as a default for various
+  # other settings. Setting it to false produces a more conservative /
+  # minimal set of defaults.
+  matter_enable_recommended = true
+}

examples/shell/shell_common/BUILD.gn

@@ -13,8 +13,7 @@
 # limitations under the License.
 
 import("//build_overrides/chip.gni")
-import("//build_overrides/openthread.gni")
-import("${chip_root}/src/lib/core/core.gni")
+import("${chip_root}/config/recommended.gni")
 import("${chip_root}/src/platform/device.gni")
 
 declare_args() {

src/app/common_flags.gni

@@ -13,7 +13,7 @@
 # limitations under the License.
 
 import("//build_overrides/chip.gni")
-import("${chip_root}/src/lib/core/core.gni")
+import("${chip_root}/config/recommended.gni")
 
 declare_args() {
   # Temporary flag for interaction model and echo protocols, set it to true to enable

src/lib/core/core.gni

@@ -12,21 +12,10 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-declare_args() {
-  # Enable recommended settings by default. This is a meta-setting
-  # that is enabled by default, and acts as a default for various
-  # other settings. Setting it to false produces a more conservative /
-  # minimal set of defaults.
-  #
-  # As additional features with their own settings are added to the SDK,
-  # consider using this meta-setting instead of a default value of 'true',
-  # especially where a different default is used based on platform (current_os):
-  # E.g. various debugging features have previously been defaulted to on
-  # for Linux and/or Mac but off for embedded platforms (on the assumption
-  # that Linux / Mac don't have resource constraints?); build settings of that
-  # nature should instead reference this meta-setting.
-  matter_enable_recommended = true
+import("//build_overrides/chip.gni")
+import("${chip_root}/config/recommended.gni")
 
+declare_args() {
   # Enable logging. Shorthand for chip_error_logging, etc.
   chip_logging = true
 }

src/tracing/tracing_args.gni

@@ -11,10 +11,8 @@
 # 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.
-import("//build_overrides/build.gni")
 import("//build_overrides/chip.gni")
-import("${build_root}/config/compiler/compiler.gni")
-import("${chip_root}/src/lib/core/core.gni")
+import("${chip_root}/config/recommended.gni")
 import("${chip_root}/src/platform/device.gni")
 
 declare_args() {