feat(test_build_system): add --buildv2 pytest option and buildv2 test app

The IDF build system v2 should be backward compatible with IDF build
system v1 in most situations. Therefore, it makes sense to reuse the
existing v1 tests and run them for v2 as well. This approach will help
ensure that v2 maintains backward compatibility. Introduce a new
--buildv2 option, which switches the existing tests to use the newly
added buildv2_test_app for v2. The goal is to enable the existing v1
tests incrementally in CI as the v2 implementation progresses.

Signed-off-by: Frantisek Hrbata <frantisek.hrbata@espressif.com>

tools/test_build_system/buildv2_test_app/CMakeLists.txt

@@ -0,0 +1,13 @@
+cmake_minimum_required(VERSION 3.22)
+
+# placeholder_before_include_project_cmake
+
+include($ENV{IDF_PATH}/tools/cmakev2/idf.cmake)
+
+# placeholder_after_include_project_cmake
+
+# FIXME: Replace the following with idf_project_default when it becomes
+# available.
+project(buildv2_test_app C CXX ASM)
+
+__generate_project_info()

tools/test_build_system/buildv2_test_app/README.md

@@ -0,0 +1 @@
+Information about this test app can be found [here](../README.md#application-under-test).

tools/test_build_system/buildv2_test_app/main/CMakeLists.txt

@@ -0,0 +1,5 @@
+# placeholder_before_idf_component_register
+
+idf_component_register(SRCS "buildv2_test_app.c"
+                       # placeholder_inside_idf_component_register
+)

tools/test_build_system/buildv2_test_app/main/Kconfig.projbuild

@@ -0,0 +1,4 @@
+# Misspelled Kconfig file checks whether it is picked up by the build system
+config FROM_MISSPELLED_KCONFIG
+    bool "From misspelled Kconfig"
+    default y

tools/test_build_system/buildv2_test_app/main/buildv2_test_app.c

@@ -0,0 +1,12 @@
+/*
+ * SPDX-FileCopyrightText: 2025 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+#include <stdio.h>
+// placeholder_before_main
+
+void app_main(void)
+{
+    // placeholder_inside_main
+}