[libc++] views::split and views::lazy_split shouldn't be range adaptor closures #75002
Description
See my analysis in #74961 followed by @cpplearner's #74961 (comment).
The views::split and views::lazy_split machinery shouldn't derive from __range_adaptor_closure:
llvm-project/libcxx/include/__ranges/split_view.h
Lines 196 to 197 in fde04e6
llvm-project/libcxx/include/__ranges/lazy_split_view.h
Lines 439 to 440 in fde04e6
Instead they should inherit from nothing, like views::take_while:
llvm-project/libcxx/include/__ranges/take_while_view.h
Lines 135 to 137 in fde04e6
I'm unsure if other changes will be needed, beyond my test changes in #74961.