* Enable running PEP8 checks via flake8 as part of the build if flake8 is installed.
Update scripts in \tools and \onnxruntime\python. Excluding \onnxruntime\python\tools which needs a lot more work to be PEP8 compliant. Also excluding orttraining\tools for the same reason.
Install flake8 as part of the static_analysis build task in the Win-CPU CI so the checks are run in one CI build.
Update coding standards doc.
* Mention OrtCreateSessionFromArray in C API doc
* Fix perf test executable due to removal of certain C APIs
* fix linux build
* Avoid duplication
* Update coding guidelines to prefer using make_unique for heap allocations (unless where not possible).
* As we consistently use non-const reference for modifiable arguments that cannot be null, update the conventions to reflect that.
Add a note on qualifying 'auto' to make the intent clearer and it easier to notice accidental copies.
* Address PR comment by adding a statement around disabling copy/assignment/move for new classes until needed.
