Ranged insert test section is added in unit-ordered_json.cpp

[YarikTH]

Fix proposal for "#2490 Missing "void insert( InputIt first, InputIt last );" overload in nlohmann::ordered_map"
This PR is in Work In Progress state

Todo:

• Add missing test case that fails
• Add proposed method implementation
• Make sure test is passed
• PR is done and ready for approval

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Pull request checklist

Read the Contribution Guidelines for detailed information.

• Changes are described in the pull request, or an existing issue is referenced.
• The test suite compiles and runs without error.
• Code coverage is 100%. Test cases can be added by editing the test suite.
• The source code is amalgamated; that is, after making changes to the sources in the include/nlohmann directory, run make amalgamate to create the single-header file single_include/nlohmann/json.hpp. The whole process is described here.

[coveralls]

Coverage remained the same at 100.0% when pulling 972c15f on YarikTH:issue2490 into d8d8cbf on nlohmann:develop.

[YarikTH]

Tests on macOS 10.13 are failed, but it doesn't connect with this PR. Something strange with the container itself.
I can't fix it due to "one fix - one PR" rule. And I have no idea how to fix container errors anyway.

[YarikTH]

Maybe this PR need additional try_compile test for exactly what I tried initially - explicitly instantiated nlohmann::json and nlohmann::ordered_json because lack of method was discovered exactly this way. It allows finding other such problems in the future. But I don't know where to place such a test. I think It doesn't match a normal test suite. Any ideas?

[nlohmann]

Looks good to me.

[nlohmann]

Thanks!