[WDF] Add Windows Driver Framework files

Takern from Microsoft GitHub repo:
d9c6040fe9

Licensed under MIT

sdk/lib/drivers/wdf/shared/support/fxregkey.cpp

@@ -0,0 +1,66 @@
+//
+//    Copyright (C) Microsoft.  All rights reserved.
+//
+#include "FxSupportPch.hpp"
+
+extern "C" {
+#if defined(EVENT_TRACING)
+#include "FxRegKey.tmh"
+#endif
+}
+
+_Must_inspect_result_
+NTSTATUS
+FxRegKey::_VerifyMultiSzString(
+    __in PFX_DRIVER_GLOBALS FxDriverGlobals,
+    __in PCUNICODE_STRING RegValueName,
+    __in_bcount(DataLength) PWCHAR DataString,
+    __in ULONG DataLength
+    )
+/*++
+
+Routine Description:
+    This static function checks the input buffer to verify that it contains
+    a multi-sz string with a double-NULL termination at the end of the buffer.
+
+Arguments:
+    DataString - buffer containing multi-sz strings. If there are no strings
+        in the buffer, the buffer should at least contain two UNICODE_NULL
+        characters.
+
+    DataLength - the size in bytes of the input buffer.
+
+Return Value:
+    STATUS_OBJECT_TYPE_MISMATCH - if the the data buffer is off odd-length,
+        or it doesnt end with two UNICODE_NULL characters.
+
+    STATUS_SUCCESS - if the buffer contains valid multi-sz strings.
+
+  --*/
+{
+    ULONG numChars;
+
+    if ((DataLength % 2) != 0) {
+        DoTraceLevelMessage(
+            FxDriverGlobals, TRACE_LEVEL_ERROR, TRACINGERROR,
+            "Reg value name %wZ, DataLength %d, Data buffer length is invalid, "
+            "STATUS_OBJECT_TYPE_MISMATCH",
+            RegValueName, DataLength);
+        return STATUS_OBJECT_TYPE_MISMATCH;
+    }
+
+    numChars = DataLength / sizeof(WCHAR);
+    if (numChars < 2 ||
+        DataString[numChars-1] != UNICODE_NULL ||
+        DataString[numChars-2] != UNICODE_NULL) {
+
+        DoTraceLevelMessage(
+            FxDriverGlobals, TRACE_LEVEL_ERROR, TRACINGERROR,
+            "Read value name %wZ, DataLength %d, Data buffer from registry does not "
+            "have double NULL terminal chars, STATUS_OBJECT_TYPE_MISMATCH",
+            RegValueName, DataLength);
+        return STATUS_OBJECT_TYPE_MISMATCH;
+    }
+
+    return STATUS_SUCCESS;
+}