Normalize file paths in LoadPaths

[jason-fugue]

This PR resolves #167. The issue was that a lot of our code produces 'clean' paths and we weren't accounting for that when we check whether or not we've already loaded a file. This was causing TF files to get loaded twice if the input path had a leading ./.

[jaspervdj-luminal]

Sort of nitpicky but I think it's a better idea to keep the paths as they are as much as possible, and move this logic to AlreadyLoaded / loadedPaths?

[jason-fugue]

Sort of nitpicky but I think it's a better idea to keep the paths as they are as much as possible, and move this logic to AlreadyLoaded / loadedPaths?

I was leaning towards doing it this way because the behavior seems more consistent afterwards. One example where it's inconsistent without that transformation is the behavior for directories with a leading ./ vs individual files:

# Pointing to ./infra_cfn/cloudformation.yaml
$ regula run ./infra_cfn/cloudformation.yaml

FG_R00092: IAM policies should not have full "*:*" administrative privileges [High]

  [1]: InvalidGroup01
       in ./infra_cfn/cloudformation.yaml:94:3

# Pointing to the ./infra_cfn directory. Somewhere down the line, os.ReadDir drops the leading ./, so the filepath becomes infra_cfn/cloudformation.yaml
$ regula run ./infra_cfn 

FG_R00092: IAM policies should not have full "*:*" administrative privileges [High]

  [1]: InvalidGroup01
       in infra_cfn/cloudformation.yaml:94:3

Preemptively applying filepath.Clean() feels a lot simpler and makes it so that the filepath looks like same whether you point to it directly or regula finds it.

Are you worried that folks would find it confusing that we dropped the ./ or do you think this could potentially cause some bugs?

[jaspervdj-luminal]

More that it could cause bugs/inconveniences for users, when they would run regula run -f json X and then index/filter by X, especially if they are not using Go and their filepath library has a subtly different Clean. But I think your justification works; we can always change this if necessary.