Implement special number and plural category changes required by CLDR-14208

This ticket tracks the ICU counterpart of CLDR the work in CLDR-14208:

In particular: is re-evaluating how negative numbers should be handled for mixed units (e.g. -10° 15', -10° -15', -11° 45' , “-5 foot 6 inches”. And any language/locale dependence for this?)

Additionally: it will investigate special compact plurals, and the correct handling of the plural forms of scientific notation. If ICU changes are necessary, this ticket either covers those, or covers the creating of new tickets for those.