Add intEnum validation to NodeValidationVisitor

[maximk000]

Background

Adds a new plugin to validate intEnums in NodeValidationVisitor. Previously you could provide values outside of the allowed set without failing validation. IntEnum Shapes also qualify as Integer Shapes, so they will pass through the same validation as Integer Shapes in validateNaturalNumber() to make sure floats aren't provided.

Testing

Added test cases:

• two for valid values defined by the intEnum
• one for wrong shape
• one for a number with a floating point, similar to Integer tests

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