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Update _MSVC_STL_UPDATE value to January 2020 - #429

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Stephan T. Lavavej (StephanTLavavej) merged 3 commits into
microsoft:masterfrom
pmisik:private/misik/stl409
Jan 24, 2020
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Update _MSVC_STL_UPDATE value to January 2020#429
Stephan T. Lavavej (StephanTLavavej) merged 3 commits into
microsoft:masterfrom
pmisik:private/misik/stl409

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@pmisik Pavol Mišík (pmisik) commented Jan 21, 2020

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Description

Implements #409

Checklist

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@BillyONeal
Optimize the is_permutation family and _Hash::operator== for multicon…
f35ed4f 
…tainers (microsoft#423)

* Optimize the is_permutation family and _Hash::operator== for multicontaniers slightly.


4660: _Find_pr is a helper for is_permutation, so move it down to that area.
4684: The SHOUTY banners were attached to functions which were implmentation details of is_permutation, so I fixed them up to say is_permutation and removed the banners for helper functions.
4711: Use if constexpr to avoid a tag dispatch call for _Trim_matching_suffixes. Optimizers will like this because they generally hate reference-to-pointer, and it also serves to workaround DevCom-883631 when this algorithm is constexprized.
4766: Indicate that we are trimming matching prefixes in this loop body, and break apart comment block that was incorrectly merged by clang-format.
4817: In the dual range forward version of the algorithm, calculate the distances concurrently to avoid wasting lots of time when the distances vary by a lot. For example, is_permutation( a forward range of length 1, a forward range of length 1'000'000 ) used to do the million increments, now it stops at 1 increment.
4862: In the dual range random-access version, avoid recalculating _Last2 when it has already been supplied to us.


1404: Move down construction of _Bucket_hi in _Equal_range to before the first loop body using it.
1918: Added a new function to calculate equality for unordered multicontainers. We loop over the elements in the left container, find corresponding ranges in the right container, trim prefixes, then dispatch to is_permutation's helper _Check_match_counts.
Improvements over the old implementation:
* For standard containers, we no longer need to hash any elements from the left container; we know that we've found the "run" of equivalent elements because we *started* with an element in that container. We also never go "backwards" or multiply enumerate _Left (even for !_Standard), which improves cache use when the container becomes large.
* Just like the dual range is_permutation improvement above, when the equal_ranges of the containers are of wildly varying lengths, this will stop on the shorter of the lengths.
* We avoid the 3-arg is_permutation doing a linear time operation to discover _Last2 that we already had calculated in determining _Right's equal_range.
The function _Multi_equal_check_equal_range tests one equal_range from the left container against the corresponding equal_range from the right container, while _Multi_equal invokes _Multi_equal_check_equal_range for each equal_range.

Performance results:

```
Benchmark	Before (ns)	After (ns)	Percent Better
HashRandomUnequal/1	18.7	11.7	59.83%
HashRandomUnequal/10	137	97	41.24%
HashRandomUnequal/100	1677	1141	46.98%
HashRandomUnequal/512	10386	7036	47.61%
HashRandomUnequal/4096	173807	119391	45.58%
HashRandomUnequal/32768	2898405	1529710	89.47%
HashRandomUnequal/100000	27441112	18602792	47.51%
HashRandomUnequal/1	18.9	11.8	60.17%
HashRandomUnequal/10	138	101	36.63%
HashRandomUnequal/100	1613	1154	39.77%
HashRandomUnequal/512	10385	7178	44.68%
HashRandomUnequal/4096	171718	120115	42.96%
HashRandomUnequal/32768	3352231	1510245	121.97%
HashRandomUnequal/100000	26532471	19209741	38.12%
HashRandomEqual/1	16	9.4	70.21%
HashRandomEqual/10	126	89.2	41.26%
HashRandomEqual/100	1644	1133	45.10%
HashRandomEqual/512	10532	7183	46.62%
HashRandomEqual/4096	174580	120029	45.45%
HashRandomEqual/32768	3031653	1455416	108.30%
HashRandomEqual/100000	26100504	19240571	35.65%
HashRandomEqual/1	15.9	9.38	69.51%
HashRandomEqual/10	123	94.1	30.71%
HashRandomEqual/100	1645	1151	42.92%
HashRandomEqual/512	10177	7144	42.46%
HashRandomEqual/4096	172994	121381	42.52%
HashRandomEqual/32768	3045242	1966513	54.85%
HashRandomEqual/100000	26013781	22025482	18.11%
HashUnequalDifferingBuckets/2	5.87	3.41	72.14%
HashUnequalDifferingBuckets/10	12	3.39	253.98%
HashUnequalDifferingBuckets/100	106	3.41	3008.50%
HashUnequalDifferingBuckets/512	691	3.46	19871.10%
HashUnequalDifferingBuckets/4096	6965	3.47	200620.46%
HashUnequalDifferingBuckets/32768	91451	3.46	2642992.49%
HashUnequalDifferingBuckets/100000	290430	3.52	8250752.27%
HashUnequalDifferingBuckets/2	5.97	3.4	75.59%
HashUnequalDifferingBuckets/10	11.8	3.54	233.33%
HashUnequalDifferingBuckets/100	105	3.54	2866.10%
HashUnequalDifferingBuckets/512	763	3.46	21952.02%
HashUnequalDifferingBuckets/4096	6862	3.4	201723.53%
HashUnequalDifferingBuckets/32768	94583	3.4	2781752.94%
HashUnequalDifferingBuckets/100000	287996	3.43	8396284.84%
```

Benchmark code:
```
#undef NDEBUG
#define _SILENCE_STDEXT_HASH_DEPRECATION_WARNINGS
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

using namespace std;

template