refactor type_cast_value

[davidism]

• Don't need recursion to validate mutliple and nargs.
• When validating value at runtime, only raise BadParameter, not TypeError or ValueError.
• Validate default value against multiple and nargs in __init__. Can't use type_cast_value on default as that can have side effects such as opening a file.
• For multiple and nargs=-1, validate that the value is iterable (and not a string). For nargs>0 validate that the length matches. For multiple and nargs>0, validate the length of each item.
• Reword error messages for consistency.
• Reword error message about "arity" since that's a technical term. For types.Tuple.convert, raise a BadParameter error and match the argument count error that Python would raise.
• For ease of validation, needed to make multiple a parameter for Parameter instead of only Option. Argument checks that it's not given.

• fixes Move iterable checks from type_cast_value to __init__ #1806

Checklist:

• Add tests that demonstrate the correct behavior of the change. Tests should fail without the change.
• Add or update relevant docs, in the docs folder and in code.
• Add an entry in CHANGES.rst summarizing the change and linking to the issue.
• Add .. versionchanged:: entries in any relevant code docs.
• Run pre-commit hooks and fix any issues.
• Run pytest and tox, no tests failed.