Add X::Invalid::ComputedValue exception
Add X::Invalid::ComputedValue exception

Purpose is to use it for conditions where argument values given to a method are
correct, but produce some invalid condition during the method's operation.

Example:

X::Invalid::ComputedValue.new(
    :name<mapper> :method<classify-list> :value('an Iterable item')
    :reason('BagHash cannot be nested and so does not support multi-level classification')
).throw;

Produces:
'mapper on classify-list computed to an Iterable item, which cannot be used because
BagHash cannot be nested and so does not support multi-level classification'

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