Elwin allow processing ILL data

[robertapplin]

Description of work

This PR makes it possible to process ILL data with a y axis in units of "Degrees" to be processed on the Elwin tab of the Inelastic Data Processor interface.

Fixes #38035

To test:

Follow the testing instructions in the attached issue. It should not error.

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[mpatrou]

It looks good to me!