nx_tzdb: Create headers from downloaded system archive data

Use lat9nq/tzdb_to_nx release data to generate header files.

nx_tzdb: Use an interface library

nx_tzdb: Gate download if achive not exists

nx_tzdb: Fix header generator brace closing

nx_tzdb: Add base directory files

nx_tzdb: Add SPDX info

externals/nx_tzdb/ListFilesInDirectory.cmake

@@ -0,0 +1,8 @@
+# SPDX-FileCopyrightText: 2023 yuzu Emulator Project
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+# CMake does not have a way to list the files in a specific directory, 
+# so we need this script to do that for us in a platform-agnostic fashion
+
+file(GLOB FILE_LIST LIST_DIRECTORIES false RELATIVE ${CMAKE_SOURCE_DIR} "*")
+execute_process(COMMAND ${CMAKE_COMMAND} -E echo "${FILE_LIST};")