Improve debugging of Mint values.

[gdotdesign]

This PR improves how Mint values (types) are printed. Before this PR, when using Debug.log or dbg the JavaScript versions of values are being printed to the console:

Which is OK, but we can do better. This PR changes that to this:

Basically, we instrument the generated code, injecting the name of the records and variants so we can pretty print them.

If we are using dbg we have a location as well (this is not new):

Other things:

• Added Debug.inspect which returns the pretty printed version.
• Debug.log remains as-is printing the raw values.
• dbg is now using the pretty printed version by default, to get the raw value we can use dbg!
• The location line is not printed if source maps are enabled because it's redundant since it will point to the source.
  

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Resolves #641.