Add ranges::{starts,ends}_with

[akukanov]

The implementations of ranges::starts_/ends_with redirect to mismatch and equal respectively, as described in the C++ standard.

[dmitriy-sobolev]

LGTM

Removing the approval because of this clang-format complaints:

-    auto begin() const
+    auto
+    begin() const
     {
         return __begin(__r) + __n;
     }
 
-    auto end() const
+    auto
+    end() const
     {
         return __end(__r);
     }

and optionally this one:

-} // __internal
+} // namespace __internal

[dmitriy-sobolev]

LGTM

Retracting my approval due to Sergey's finding.

        using _DistanceType = std::ranges::range_difference_t<_R1>;
        _DistanceType __n1 = std::ranges::distance(__r1);
        _DistanceType __n2 = std::ranges::distance(__r2); // <- May truncate __n2

        if (__n1 < __n2) // <- this check will not work properly if __n2 is truncated. 
            return false;

[SergeyKopienko]

LGTM