Source generated interop should be unconditionally ExactSpelling=true

[jkotas]

Repro:

Inspect source generated interop for CoreLib

Actual behavior:

Some DllImports have ExactSpelling=false and other have ExactSpelling=true

[System.Runtime.InteropServices.DllImportAttribute("kernel32.dll", EntryPoint = "GetThreadPriority", ExactSpelling = false)]
extern static unsafe global::Interop.Kernel32.ThreadPriority __PInvoke__(System.IntPtr hThread);

[System.Runtime.InteropServices.DllImportAttribute("kernel32.dll", EntryPoint = "CreateThreadpoolIo", ExactSpelling = true)]
extern static unsafe System.IntPtr __PInvoke__(System.IntPtr fl, delegate* unmanaged<global::System.IntPtr, global::System.IntPtr, global::System.IntPtr, uint, global::System.UIntPtr, global::System.IntPtr, void> pfnio, global::System.IntPtr context, global::System.IntPtr pcbe);

Expected behavior:

All DllImports have ExactSpelling=true

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Issue Details

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Repro: Inspect source generated interop for CoreLib

Actual behavior: Some DllImports have ExactSpelling=false and other have ExactSpelling=true

            [System.Runtime.InteropServices.DllImportAttribute("kernel32.dll", EntryPoint = "GetThreadPriority", ExactSpelling = false)]
            extern static unsafe global::Interop.Kernel32.ThreadPriority __PInvoke__(System.IntPtr hThread);

            [System.Runtime.InteropServices.DllImportAttribute("kernel32.dll", EntryPoint = "CreateThreadpoolIo", ExactSpelling = true)]
            extern static unsafe System.IntPtr __PInvoke__(System.IntPtr fl, delegate* unmanaged<global::System.IntPtr, global::System.IntPtr, global::System.IntPtr, uint, global::System.UIntPtr, global::System.IntPtr, void> pfnio, global::System.IntPtr context, global::System.IntPtr pcbe);

Expected behavior: All DllImports have ExactSpelling=true

Author:	jkotas
Assignees:	-
Labels:	area-System.Runtime.InteropServices
Milestone:	-