`<ranges>`: Implement `ranges::to`, guarded by `__cpp_lib_ranges_to_container`.

The following are all guarded  by `__cpp_lib_containers_ranges`:
`<xmemory>`: Generalize `_Uninitialized_copy` to iterator+sentinel ranges; add `_Uninitialized_copy_n` for counted ranges. Implement `from_range_t`, `from_range`, and exposition-only helper concepts / type aliases.
`<xutility>`: Promote `_Get_final_iterator_unwrapped` here from `<algorithm>`. Add `_Copy_memmove_n` (`_Copy_n_unchecked`), similar to `_Copy_memmove` (resp. `_Copy_unchecked`) but for counted ranges. Generalize `_Iter_copy_cat` to `_Sent_copy_cat`.
`<memory>`: Use `_Copy_memmove_n` (see `<xutility>`) as appropriate.

`<yvals_core.h>`: `_HAS_CXX23` controls P1206R7, define `__cpp_lib_containers_ranges` and `__cpp_lib_ranges_to_container`.

`<deque>`: Implement `from_range_t` constructor(s) and corresponding deduction guide(s), `prepend_range`, `append_range`, `assign_range`, and `insert_range`.
`<forward_list>`: Implement `from_range_t` constructor(s) and corresponding deduction guide(s), `prepend_range`, `assign_range`, and `insert_range_after`.
`<list>`: Implement `from_range_t` constructor(s) and corresponding deduction guide(s), `prepend_range`, `append_range`, `assign_range`, and `insert_range`.
`<map>` and `<set>`: For both `map`, `multimap`, `set`, and `multiset`, implement `from_range_t` constructor(s) and corresponding deduction guide(s). (Inherit `insert_range` from `_Tree`.)
`<queue>`: For both `queue` and `priority_queue`, implement `from_range_t` constructor(s) and corresponding deduction guide(s), and `push_range`. (I've speculatively implemented `priority_queue::push_range` by calling `append_range` on the container per the resolution I've proposed for an LWG issue I submitted specifically to allow implementation via `append_range`.)
`<stack>`: Implement `from_range_t` constructor(s) and corresponding deduction guide(s), and `push_range`.
`<unordered_map>` and `<unordered_set>`: For both `unordered_map`, `unordered_multimap`, `unordered_set`, and `unordered_multiset`, implement `from_range_t` constructor(s) and corresponding deduction guide(s). (Inherit `insert_range` from `_Hash`.)
`<vector>`: For both `vector` and `vector<bool>`, implement `from_range_t` constructor(s) and corresponding deduction guide(s), `append_range`, `assign_range`, and `insert_range`.
`<xstring>`: For both `basic_string`, implement `from_range_t` constructor(s) and corresponding deduction guide(s), `append_range`, `assign_range`, `insert_range`, and `replace_with_range`.

Test both new feature-test macros in `tests/std/tests/VSO_0157762_feature_test_macros`.
Test all new deduction guides in `tests/std/tests/P0433R2_deduction_guides`.
Test `_Copy_n_unchecked` in `tests/std/tests/P0784R7_library_machinery`.
Add new t`P1206R7_{container}_{operation}` "range algorithm"-style tests for each new container (or container adapter) member function.
Add new `P1206R7_from_range` test for `from_range` and `from_range_t`.
Add new `P1206R7_ranges_to` test for `ranges::to`.

Fixes microsoft#2532.

…_after(pos, first, last)

... per resolution of just-submitted LWG issue.