Fix IAT Reconstruction

[Catminusminus]

This will be fix #523

Currently, this->binary_->section_from_offset(offset_imports) is used as the original import section.
However, if the "backward shift" (explained in #523 ) happens, this returns the previous section of the original import section. So I try another way to obtain the original import section.

I introduce PE_SECTION_TYPES::OLD_IMPORT type to mark the original import section.
The type will be added to the target section when the PE_SECTION_TYPES::IMPORT type will be removed from it.

After adding the new import section, we can find the original import section by looking to see if the type is PE_SECTION_TYPES::OLD_IMPORT.

If we can not find the original import section, it will fall back to the current implementation, that is, this->binary_->section_from_offset(offset_imports) will be used.

macOS and iOS CI jobs currently failed, but I suspect that they are due to the GitHub Actions' issue (actions/runner-images#841).
In fact, I see the "(X) This check failed" message and these jobs are unstable...
https://github.com/Catminusminus/LIEF/actions/runs/492792964

Sorry if I my suspicions are wrong. I'll re-run the jobs to find out what's wrong, anyway.

[Catminusminus]

I found this PR works for C++, but doesn't work for Python API. That is, applying the following code 9 times creates an invalid PE file.

    binary = lief.PE.parse(input_path)
    binary.optional_header.dll_characteristics &= (
        ~lief.PE.DLL_CHARACTERISTICS.DYNAMIC_BASE
    )
    builder = lief.PE.Builder(binary)
    builder.build_imports(True).patch_imports(True)
    builder.build()
    builder.write(output_path)

I'm investigating this issue.

[Catminusminus]

The above my comment is wrong and I conformed that this PR do work for Python API.
I'm sorry for my misunderstanding.