feat: PDB import via RawPDB, no msdia140.dll dependency

Replace DIA SDK COM-based PDB importer with RawPDB (MolecularMatters)
which reads PDB files directly via memory-mapped I/O. Adds File menu
"Import PDB..." dialog with type filtering, selection, and progress.

- Vendor raw_pdb into third_party/
- Two-phase API: enumeratePdbTypes() + importPdbSelected()
- Full recursive import of structs/unions/arrays/pointers/bitfields
- PDB import dialog with name filter, select-all, type count
- Benchmark: 1654 types from ntkrnlmp.pdb in 16ms
- Reorganize import/export files into src/imports/

third_party/raw_pdb/src/PDB_ErrorCodes.h

@@ -0,0 +1,26 @@
+// Copyright 2011-2022, Molecular Matters GmbH <office@molecular-matters.com>
+// See LICENSE.txt for licensing details (2-clause BSD License: https://opensource.org/licenses/BSD-2-Clause)
+
+#pragma once
+
+#include "Foundation/PDB_Macros.h"
+
+
+namespace PDB
+{
+	enum class PDB_NO_DISCARD ErrorCode : unsigned int
+	{
+		Success = 0u,
+
+		// main PDB validation
+		InvalidDataSize,
+		InvalidSuperBlock,
+		InvalidFreeBlockMap,
+
+		// stream validation
+		InvalidStream,
+		InvalidSignature,
+		InvalidStreamIndex,
+		UnknownVersion
+	};
+}