Fix ValidationError.formatError() clobbering path param

[shaungrady]

Changes

• ValidationError.formatError() overwrites path with a more friendly label string (if defined) for more friendly error message interpolation; however, this causes the path data to be lost entirely.
  • Rather than undertake refactoring this logic and cause a breaking change, where using alternative values for interpolating ${path} within error strings should arguably be a concern that's left to the message function, I opted to simply create a new params property—originalPath—for recording this value.
• Update MessageParams type with originalPath: string; property
• Add MessageParams and AnyMessageParams to library exports
  • I couldn't see a reason why these types are private, and I'd certainly love to make use of them.

[jquense]

thanks!