This commit ads the corresponding --output-file option from idf_size.py to idf.py.
This is needed because piping the idf.py size output to a file would result in CMake output being present in the file as well.
This adds CSV support to idf_size.py and idf.py size actions and using the --format argument which accepts 'text', 'json' or 'csv' as input.
idf_size.py --json argument is deprecated but left to avoid a breaking change.
For idf.py size actions OUTPUT_JSON environment variable set at configuration time is overriden at target build time if --format is used.
Additionally, this commit refactors big parts of code, unified usage of json_dict and manually generated dictionaries for textual output and improves code quality in many parts.
This moves all the documentation relating to using idf.py out of the build system documentation in order to declutter and more logically group the documentation.
It is now present in the tools page under IDF Frontend - idf.py.
Additionally there has been lots of rewriting and some minor fixes on the way.
