Normalize files paths

[danilowoz]

Tell us how you think we can improve Sandpack

Standardize and normalize the files paths provide by:

• Templates;
• Files props;
• External sandboxes (future feature #347);
• Package.json creation;

How would your idea work?

• Add leading slash;
• Remove leading dot (?);
• Make sure it doesn't affect activePath and openPaths;

What are invalid and valid file paths you can pass to files object?

Valid:

• "./";
• "/foo.ts";
• "/foo" no extension;
• "foo.ts" no leading;

Invalid

• "/"
• "..."
• "..fooo"