Avoid duplicate loading of component files

As discovered in ComplianceAsCode#11190,
the `components.load()` function is called many times during a build
of product content. However, the component files need to be loaded only
once.

When the build systems resolves the content using `compile_all.py`, the
`compile_all.py` creates an instance of `ssg.builld_yaml.BuildLoader`
class.  Moreover, many other instances of `ssg.builld_yaml.BuildLoader`
class are created recursively as the loader recurses into
sub-directories of the given benchmark root directory.  When we iterate
over the directories, for each child directory the script creates a new
instance of the `ssg.build_yaml.BuildLoader` by the
`ssg.builld_yaml.BuildLoader._get_new_loader()` method. This method
should ensure that the component data and other data won't be
unnecessarily loaded again but will be just referenced from the parent
`ssg.builld_yaml.BuildLoader` that handles the parent directory.

The problem is the way how the
`ssg.builld_yaml.BuildLoader._load_components()` method is called in the
ctor of `ssg.builld_yaml.BuildLoader`. The ctor is called before
the initialization of the `rule_to_components` attribute. Also, there is
no code in this ctor or elsewhere assuring that it won't load the
components data if they were already loaded.

In this commit, we won't call `_load_components` in the ctor, which will
leave the opportunity to `_get_new_loader` to swap the data as the comment
said.

This should bring a speed up about 5 seconds.

build-scripts/compile_all.py

@@ -133,6 +133,7 @@ def main():
 
     loader = ssg.build_yaml.BuildLoader(
         None, env_yaml, product_cpes, args.sce_metadata, args.stig_references)
+    loader.load_components()
     load_benchmark_source_data_from_directory_tree(loader, env_yaml, product_yaml)
 
     project_root_abspath = os.path.abspath(args.project_root)

ssg/build_yaml.py

@@ -1331,19 +1331,18 @@ def __init__(
         if stig_reference_path:
             self.stig_references = ssg.build_stig.map_versions_to_rule_ids(stig_reference_path)
         self.components_dir = None
-        self.rule_to_components = self._load_components()
+        self.rule_to_components = None
 
-    def _load_components(self):
+    def load_components(self):
         if "components_root" not in self.env_yaml:
             return None
         product_dir = self.env_yaml["product_dir"]
         components_root = self.env_yaml["components_root"]
         self.components_dir = os.path.abspath(
             os.path.join(product_dir, components_root))
         components = ssg.components.load(self.components_dir)
-        rule_to_components = ssg.components.rule_component_mapping(
+        self.rule_to_components = ssg.components.rule_component_mapping(
             components)
-        return rule_to_components
 
     def _process_values(self):
         for value_yaml in self.value_files: