feat(cmakev2/idf): add __init_idf_version to set IDF_VER

Initialize the IDF_VER build property using the version.txt file, or use
git-describe. If neither is available, fall back to the value of the
IDF_VERSION environment variable.

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

tools/cmakev2/test/CMakeLists.txt

@@ -58,7 +58,7 @@ function(test_component_priority)
     __dump_component_properties("${component_name}")
 endfunction()
 
-# Test that IDF_VERSION is set
+# Test that IDF_VERSION and IDF_VER build property is set
 function(test_idf_version)
     if(NOT DEFINED IDF_VERSION_MAJOR OR
             NOT DEFINED IDF_VERSION_MINOR OR
@@ -66,6 +66,10 @@ function(test_idf_version)
             NOT DEFINED ENV{IDF_VERSION})
         idf_die("IDF_VERSION not set")
     endif()
+    idf_build_get_property(idf_ver IDF_VER)
+    if(NOT idf_ver)
+        idf_die("IDF_VER build property not set")
+    endif()
 endfunction()
 
 # Test that Python interpreter is set