Supporting Unit Constants in CLDR v44

[Younies Mahmoud]

Dear ICU Committee,

This Thursday, I would like to discuss proposed API changes to support the new unit constants being introduced in CLDR v44. This feature allows for more flexible unit definitions, such as "liter-per-100-kilometer" or "portion-per-1e9."

To accommodate this new functionality, I am proposing:

• Adding new API for `MeasureUnit` class: This will enable handling the constants of the units.
• Introduction of `UnitConstant` class: This new class will represent the constant values within the units.

You can find the design doc here:
https://docs.google.com/document/d/12Cx_MeaeOdaVfuhtdqLR1GKM7egU_W7h3kxejv7eH7U/edit?tab=t.0#heading=h.o0tlmwpq5rt8 

Best regards,

Younies