[libc++] Optimize __tree copy/move constructor/assignment with allocator (#163558)
This patch applies the same optimization as implemented in #151304 to
the overloads taking an allocator as the second argument.
Apple M4:
```
Benchmark old new Difference % Difference
----------------------------------------------------------- -------------- -------------- ------------ --------------
std::map<int,_int>::ctor(&&,_different_allocs)/0 14.59 12.78 -1.81 -12.41%
std::map<int,_int>::ctor(&&,_different_allocs)/1024 16407.05 6265.11 -10141.94 -61.81%
std::map<int,_int>::ctor(&&,_different_allocs)/32 395.99 199.76 -196.23 -49.56%
std::map<int,_int>::ctor(&&,_different_allocs)/8192 141478.67 53767.84 -87710.83 -62.00%
std::map<int,_int>::ctor(const&,_alloc)/0 12.83 12.71 -0.12 -0.94%
std::map<int,_int>::ctor(const&,_alloc)/1024 9979.71 7849.11 -2130.59 -21.35%
std::map<int,_int>::ctor(const&,_alloc)/32 283.82 266.05 -17.77 -6.26%
std::map<int,_int>::ctor(const&,_alloc)/8192 81418.63 63190.41 -18228.21 -22.39%
std::map<std::string,_int>::ctor(&&,_different_allocs)/0 14.58 12.68 -1.90 -13.00%
std::map<std::string,_int>::ctor(&&,_different_allocs)/1024 19513.56 7806.04 -11707.52 -60.00%
std::map<std::string,_int>::ctor(&&,_different_allocs)/32 477.80 247.28 -230.52 -48.25%
std::map<std::string,_int>::ctor(&&,_different_allocs)/8192 504558.78 69592.21 -434966.56 -86.21%
std::map<std::string,_int>::ctor(const&,_alloc)/0 12.64 12.60 -0.04 -0.33%
std::map<std::string,_int>::ctor(const&,_alloc)/1024 43198.53 37220.54 -5977.99 -13.84%
std::map<std::string,_int>::ctor(const&,_alloc)/32 928.39 867.03 -61.36 -6.61%
std::map<std::string,_int>::ctor(const&,_alloc)/8192 461313.81 389200.82 -72112.99 -15.63%
```
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