P1068R11 `ranges::generate_random`

[StephanTLavavej]

WG21-P1068R11 ranges::generate_random
LWG-4085 ranges::generate_random's helper lambda should specify the return type

Feature-test macro (adjusted by cplusplus/draft#6904):

#define __cpp_lib_ranges_generate_random 202403L

Note: We're focused on implementing the remaining library-only features in C++23. Until that's done, we will NOT be accepting PRs for C++26 features.