add libiconv port

[emmatyping]

Here is a working port of libiconv.

Potential issues (not really road blockers more of style):

• patch instead of using a custom file? I chose to use a custom file as the config.in since the file() command in CMake doesn't overwrite filenames. The vcpkg apply patch doesn't seem to work as it takes the out parameter as an input parameter (I can file an issue on this), and overwriting the file doesn't require git.
• patch-ify everything? The idea being that one patch would need to be applied instead of several copy commands.

I can adjust this PR based on your feedback.

[msftclas]

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[msftclas]

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[ras0219-msft]

This looks pretty perfect as-is 👍 . My thoughts are

• If you only need to add files, don't use a patch.
• Do not modify files by checking in a modified copy -- always use a patch.
• If you need to add files and modify files, you're welcome to select the mix that works the best for you (I generally find patches easier to work with in this case).

[emmatyping]

Thanks. I will start working on a libxml2 port with those guidelines in mind.