ICU-21763 UVector cleanup, continued.

ICU-21763 UVector cleanup, continued.

Revise uses of UVector in the next batch of files to better handle memory
allocation failures.  This is one of an ongoing series of commits to address
similar problems with UVector usage throughout ICU.

The changes primarily involve switching uses of UVector::addElementX() to the
new adoptElement() or addElement() functions, as appropriate, and using
LocalPointers for tracking memory ownership.