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_NamesStream.h

@@ -0,0 +1,48 @@
+// 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"
+#include "PDB_Types.h"
+#include "PDB_CoalescedMSFStream.h"
+
+
+namespace PDB
+{
+	class RawFile;
+
+	struct NamesHeader
+	{
+		uint32_t magic;
+		uint32_t hashVersion;
+		uint32_t size;
+	};
+
+	class PDB_NO_DISCARD NamesStream
+	{
+	public:
+		NamesStream(void) PDB_NO_EXCEPT;
+		explicit NamesStream(const RawFile& file, uint32_t streamIndex) PDB_NO_EXCEPT;
+
+		PDB_DEFAULT_MOVE(NamesStream);
+
+		// Returns the header of the stream.
+		PDB_NO_DISCARD inline const NamesHeader* GetHeader(void) const PDB_NO_EXCEPT
+		{
+			return m_header;
+		}
+
+		PDB_NO_DISCARD inline const char* GetFilename(uint32_t filenameOffset) const PDB_NO_EXCEPT
+		{
+			return m_stringTable + filenameOffset;
+		}
+
+	private:
+		CoalescedMSFStream m_stream;
+		const NamesHeader* m_header;
+		const char* m_stringTable;
+
+		PDB_DISABLE_COPY(NamesStream);
+	};
+}