Add way a way to bypass msbuild csproj validation.

[belav]

The changes in #490 can slow down csharpier. On the insite-commerce repo it adds 1s to the ~30s formatting time. Should the validation be opt in? Or should there be an option to opt out? I am leaning opt-out, because most projects won't contain ~200 csproj files and ~14k cs files. The option could exist in the csharpierrc file, or it could be part of the cli options.