As described in T98943, this commit adds a node that can
evaluate a field on a separate domain in a larger field context.
This is potentially useful in many cases, to avoid relying on
a separate capture attribute node, which can make it easier
to build reusable fields that don't need geometry inputs.
Internally, the node just evaluates the input field in the larger
field context and then uses the generic domain interpolation,
so the code is simple. One future optimization might be using
the input selection to only evaluate part of the input field, but
then the selection has to be interpolated as well, and that might
not always be worth it.
For example, here the node is used to retrieve the curve index when setting the position of control points:
