* Unified environment modifications in config files
fixes#13357
This commit factors all the code that is involved in
the validation (schema) and parsing of environment modifications
from configuration files in a single place. The factored out
code is then used for module files and compiler configuration.
Attributes were separated by dashes in `compilers.yaml` files and
by underscores in `modules.yaml` files. This PR unifies the syntax
on attributes separated by underscores.
Unit testing of environment modifications in compilers
has been refactored and simplified.
b9629c36f2