Some extended attributes are supported but have no test coverage

[domenic]

In particular:

• [Clamp]
• [EnforceRange]
• [LegacyNoInterfaceObject]
• [LegacyOverrideBuiltins]
• [PutForwards]

[ExE-Boss]

Same with [Replaceable] and probably a few others.

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Also, [LegacyLenientThis] currently has a bug where the getter (and setter) will be invoked regardless of whether or not esValue implements the interface, I’m fixing that in #209.

[domenic]

I've renamed this issue and updated the OP to cover all untested extended attributes.