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/Foundation/PDB_Platform.h

@@ -0,0 +1,45 @@
+// 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
+
+
+// determine the compiler/toolchain used
+#if defined(__clang__)
+#	define PDB_COMPILER_MSVC				0
+#	define PDB_COMPILER_CLANG				1
+#	define PDB_COMPILER_GCC					0
+#elif defined(_MSC_VER)
+#	define PDB_COMPILER_MSVC				1
+#	define PDB_COMPILER_CLANG				0
+#	define PDB_COMPILER_GCC					0
+#elif defined(__GNUC__)
+#	define PDB_COMPILER_MSVC				0
+#	define PDB_COMPILER_CLANG				0
+#	define PDB_COMPILER_GCC					1
+#else
+#	error("Unknown compiler.");
+#endif
+
+// check whether C++17 is available
+#if __cplusplus >= 201703L
+#	define PDB_CPP_17						1
+#else
+#	define PDB_CPP_17						0
+#endif
+
+// define used standard types
+typedef decltype(sizeof(0)) size_t;
+static_assert(sizeof(sizeof(0)) == sizeof(size_t), "Wrong size.");
+
+typedef int int32_t;
+static_assert(sizeof(int32_t) == 4u, "Wrong size.");
+
+typedef unsigned char uint8_t;
+static_assert(sizeof(uint8_t) == 1u, "Wrong size.");
+
+typedef unsigned short uint16_t;
+static_assert(sizeof(uint16_t) == 2u, "Wrong size.");
+
+typedef unsigned int uint32_t;
+static_assert(sizeof(uint32_t) == 4u, "Wrong size.");