Allow preventing "Enum from integer" coercion using new CoercionConfig system

[cowtowncoder]

(follow-up for #2750 )

One coercion that has been problematic (and configuration setting was been requested for) is that of accepting integer value, assumed to be used as the index of Enum. While this can be efficient representation it can be brittle (as index can change if Enums are reordered in class definition) and cause invalid content to be accepted.

Configuration should probably be of form:

    // to prevent for ALL enums:
    mapper.coercionConfigFor(LogicalType.Enum)
        .setCoercion(CoercionInputShape.Integer, CoercionAction.Fail)
    // or individual type
    mapper.coercionConfigFor(MyEnum.class)
        .setCoercion(CoercionInputShape.Integer, CoercionAction.Fail)

Note, too, that this should allow alternatives of AsEmpty (default value, if specified, otherwise... null?) and AsNull.