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_ModuleSymbolStream.cpp

@@ -0,0 +1,61 @@
+// 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)
+
+#include "PDB_PCH.h"
+#include "PDB_ModuleSymbolStream.h"
+#include "PDB_RawFile.h"
+
+
+// ------------------------------------------------------------------------------------------------
+// ------------------------------------------------------------------------------------------------
+PDB::ModuleSymbolStream::ModuleSymbolStream(void) PDB_NO_EXCEPT
+	: m_stream()
+{
+}
+
+
+// ------------------------------------------------------------------------------------------------
+// ------------------------------------------------------------------------------------------------
+PDB::ModuleSymbolStream::ModuleSymbolStream(const RawFile& file, uint16_t streamIndex, uint32_t symbolStreamSize) PDB_NO_EXCEPT
+	: m_stream(file.CreateMSFStream<CoalescedMSFStream>(streamIndex, symbolStreamSize))
+{
+	// https://llvm.org/docs/PDB/ModiStream.html
+	// struct ModiStream {
+	//	uint32_t Signature;
+	//	uint8_t Symbols[SymbolSize - 4];
+	//	uint8_t C11LineInfo[C11Size];
+	//	uint8_t C13LineInfo[C13Size];
+	//	uint32_t GlobalRefsSize;
+	//	uint8_t GlobalRefs[GlobalRefsSize];
+	// };
+	// we are only interested in the symbols, but not the line information or global refs.
+	// the coalesced stream is therefore only built for the symbols, not all the data in the stream.
+	// this potentially saves a lot of memory and performance on large PDBs.
+}
+
+
+// ------------------------------------------------------------------------------------------------
+// ------------------------------------------------------------------------------------------------
+PDB_NO_DISCARD const PDB::CodeView::DBI::Record* PDB::ModuleSymbolStream::FindRecord(CodeView::DBI::SymbolRecordKind kind) const PDB_NO_EXCEPT
+{
+	// ignore the stream's 4-byte signature
+	size_t offset = sizeof(uint32_t);
+
+	// parse the CodeView records
+	while (offset < m_stream.GetSize())
+	{
+		// https://llvm.org/docs/PDB/CodeViewTypes.html
+		const CodeView::DBI::Record* record = m_stream.GetDataAtOffset<const CodeView::DBI::Record>(offset);
+		if (record->header.kind == kind)
+		{
+			return record;
+		}
+
+		const uint32_t recordSize = GetCodeViewRecordSize(record);
+
+		// position the module stream offset at the next record
+		offset = BitUtil::RoundUpToMultiple<size_t>(offset + sizeof(CodeView::DBI::RecordHeader) + recordSize, 4u);
+	}
+
+	return nullptr;
+}