Optionally write generated file when generated code is not valid (fmt error)

[valichek]

Currently if generated code is not valid and fmt returns error, invalid code is written to stderr, so there should be additional steps executed to understand the problem - like passing output to .go file, cutting the actual error and checking IDE/editor highlights. The flow appears a bit redundant.

Would be nice to have an option to keep invalid generated code in output file as configured, maybe add postfix _err to filename to indicate problem, resulting to smth like component_gen_err.go