Fix TypeUtils.makeNullableAsSpecified for SimpleTypeWithEnhancement and
FlexibleTypeWithEnhancement: change nullability of enhancement too. This
fixes several false-positive warnings, like in KT-20855 and KT-20466.
Note that it removes warning in some cases (see testdata change for
uselessElvisRightIsNull.kt). However, this removes warning about
*unnecessary* elvis, i.e. this fixed introduces weak false-negatives, which
is acceptable for the moment.
#KT-20855 Fixed Target versions 1.2.30
#KT-20466 Fixed Target versions 1.2.30
#KT-21238 Fixed Target versions 1.2.30
Dmitry Savvinov