[mlir][transform] Add PackedOrDynamicIndexList helper

[springerm]

Summary

This custom parser/printer is similar to DynamicIndexList, but has special syntax for the case where one handle represents the entire list.

Example:

// Regular index list
[10, 20, %val]

// Packed handle (no square parentheses)
%val

[ftynse]

mlir/lib/Dialect/Linalg/TransformOps/LinalgTransformOps.cpp

1580

Nit: why is integer capitalized in the message?