CsWin32 doesn't use EntryPoints provided by metadata

[riverar]

Actual behavior

Added a reference to custom metadata via ProjectionMetadataWinmd (see #356).

Metadata contains:

[DllImport("my.dll", EntryPoint = "#100", ExactSpelling = true, PreserveSig = false)]
public static extern ReturnType function();

CsWin32 generates:

[DllImport("my.dll", ExactSpelling = true)]
[DefaultDllImportSearchPaths(DllImportSearchPath.System32)]
internal static extern winmdroot.ReturnType function();

Expected behavior

CsWin32 to read/carry over the entry point as defined by metadata. This can differ from the function name (e.g. FileIconInit).

Repro steps

TBD

Context

• CsWin32 version: [e.g. 0.3.2-beta]
• Win32Metadata version (if explicitly set by project):
• Target Framework: [e.g. net6.0-windows10.0.17763.0]
• LangVersion (if explicitly set by project): [e.g. 9]