tools: Prefer python3 during install and export

Install and export script should work on systems without "python"
executable.

Closes https://github.com/espressif/esp-idf/pull/6471

Closes https://github.com/espressif/esp-idf/issues/6532

Related to https://github.com/espressif/esp-idf/issues/6421 and
https://github.com/espressif/arduino-esp32/issues/4717

export.sh

@@ -79,11 +79,14 @@ idf_export_main() {
 
     old_path="$PATH"
 
+    echo "Detecting the Python interpreter"
+    . "${IDF_PATH}/tools/detect_python.sh"
+
     echo "Adding ESP-IDF tools to PATH..."
     # Call idf_tools.py to export tool paths
     export IDF_TOOLS_EXPORT_CMD=${IDF_PATH}/export.sh
     export IDF_TOOLS_INSTALL_CMD=${IDF_PATH}/install.sh
-    idf_exports=$("${IDF_PATH}/tools/idf_tools.py" export) || return 1
+    idf_exports=$("$ESP_PYTHON" "${IDF_PATH}/tools/idf_tools.py" export) || return 1
     eval "${idf_exports}"
 
     echo "Using Python interpreter in $(which python)"
@@ -125,6 +128,7 @@ idf_export_main() {
     unset path_entry
     unset IDF_ADD_PATHS_EXTRAS
     unset idf_exports
+    unset ESP_PYTHON
 
     # Not unsetting IDF_PYTHON_ENV_PATH, it can be used by IDF build system
     # to check whether we are using a private Python environment