Unmanaged exports in AsmResolver.DotNet

[Washi1337]

Problem Description

The CLR supports exporting managed methods as unmanaged functions that can be referenced by other native binaries or being P/Invoked. Currently, there is no way in AsmResolver.DotNet to specify that a MethodDefinition should be exported.

Proposal

Add a property to MethodDefinition that indicates the method should be exported or not. The ManagedPEImageBuilder would then add the appropriate VTable fixup and export directory entries to the image.

This could look something like the following:

MethodDefinition method = ...

// Indicate method should be exported by name.
method.ExportInfo = new UnmanagedExportInfo
{
   Name = "MyExportedFunctionName",
};

// Indicate method should be exported by ordinal.
method.ExportInfo = new UnmanagedExportInfo
{
   Ordinal = 1234,
};

Alternatives

Users of AsmResolver could first transform the ModuleDefinition they are working with to a PEImage first, to then manually create and add the appropriate VTable fixup and export directory entries before writing it to the disk. This adds a lot of noise to the code, which is something we want to solve with this proposal.

Additional context

Requires #63, #179