<vector>: VS 2019 ignores explicit keyword

Describe the bug
STL allows range-based insertion to vector (and other containers) thru implicit conversion operator

Command-line test case

d:\Temp2>type repro.cpp
#include <algorithm>
#include <iostream>
#include <vector>

class test
{

};

class no_implicit_convertion
{
public:

        //Here, there is no implicit convertion from one type to another,

        //however, VS2017 ignores explicit keyword.
        explicit no_implicit_convertion(test)
        {
                std::cout << "Inserted test with implicit conversion!" << std::endl;
        }
};

int main()
{
        std::vector<no_implicit_convertion> target_vec;
        std::vector<test> test_vec{ {},{},{} };

        target_vec.insert(target_vec.end(), test_vec.begin(), test_vec.end());
}


d:\Temp2>cl /EHsc /W4 repro.cpp
Microsoft (R) C/C++ Optimizing Compiler Version 19.27.29009.1 for x86
Copyright (C) Microsoft Corporation.  All rights reserved.

repro.cpp
Microsoft (R) Incremental Linker Version 14.27.29009.1
Copyright (C) Microsoft Corporation.  All rights reserved.

/out:repro.exe
repro.obj

d:\Temp2>.\repro.exe
Inserted test with implicit conversion!
Inserted test with implicit conversion!
Inserted test with implicit conversion!

Expected behavior
Should not compile

STL version

Microsoft Visual Studio Professional 2019 Preview
Version 16.7.0 Preview 3.1

Additional context
Also tracked by DevCom-275079 and VSO-636498 / AB#636498

Begin with the repro.cpp command-line test case and the vector::insert range call using an explicit converting constructor. Compare the observed MSVC 2019 behavior with the expected compilation failure, then identify the STL implementation and regression tests covering range insertion. Done means the test no longer compiles as shown and the relevant test suite passes.