Add temporary IR nodes to typeMap

[mihaibudiu]

Fixes #2958

[mihaibudiu]

@kostasyrmia please review this; it looks like the bug is in your code.

[kostasyrmia]

Yes, you are right, this is definitely in my code.

I tried to avoid inserting these temporary fields into the typeMap, but it seems it has to be done...

The only thing that I would do additionally is removing dst_type and src_type from the signature of processHeadersInAssignment, because they no longer have any usage now that everything is in the typeMap.

I think that this:

void processHeadersInAssignment(const IR::Expression* dst, const IR::Expression* src,
                                    const IR::Type* dst_type, const IR::Type* src_type) {
    // code inside the function
}

can be changed to something like this:

void processHeadersInAssignment(const IR::Expression* dst, const IR::Expression* src) {
    auto dst_type = typeMap->getType(dst, true);
    auto src_type = typeMap->getType(src, true);

    // code inside the function
}

But also it's okay for me as it is.

Thank you for the fix!