machine: add tool to check consistency with documentation

[aykevl]

This tool checks whether the machine package matches the documentation in https://tinygo.org/docs/reference/machine/.

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This is very much a draft. Right now it only checks for constants (not even functions, types, methods, etc) and there are many things that need to be changed for this to pass all tests.

• Many constants need to be documented on tinygo.org.
• Many other constants need to be made private, because they are only to be used within the machine package.
• Some constants that are considered valid here (like ParityNone) aren't actually documented yet, this must be done before this PR is ready.

The first step in fixing this is #3169.