Fixes regression in Qt's CMake translation API.

Bug reported here:
qt5_create_translation breaks projects with multiple same-named ts files
https://bugreports.qt.io/browse/QTBUG-113152

Backport of upstream patch:
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=270868#c4
https://people.freebsd.org/~tcberner/patches/0001-Qt-Update-Qt5-to-5.15.9.patch.v2

diff -Nuar a/src/linguist/Qt5LinguistToolsMacros.cmake b/src/linguist/Qt5LinguistToolsMacros.cmake
--- a/src/linguist/Qt5LinguistToolsMacros.cmake	2023-05-04 00:46:05.642493619 +0000
+++ b/src/linguist/Qt5LinguistToolsMacros.cmake	2023-05-04 00:46:47.654701946 +0000
@@ -96,6 +96,13 @@
           file(WRITE ${_ts_lst_file} "${_lst_file_srcs}")
         endif()
         set(stamp_file "${stamp_file_dir}/${_ts_name}.stamp")
+        file(RELATIVE_PATH _ts_relative_path ${CMAKE_CURRENT_SOURCE_DIR} ${_ts_file})
+        string(REPLACE "../" "__/" _ts_relative_path "${_ts_relative_path}")
+        set(stamp_file "${stamp_file_dir}/${_ts_relative_path}.stamp")
+        get_filename_component(full_stamp_file_dir "${stamp_file}" DIRECTORY)
+        if(NOT EXISTS "${full_stamp_file_dir}")
+            file(MAKE_DIRECTORY "${full_stamp_file_dir}")
+        endif()
         add_custom_command(OUTPUT ${stamp_file}
             COMMAND ${Qt5_LUPDATE_EXECUTABLE}
             ARGS ${_lupdate_options} "@${_ts_lst_file}" -ts ${_ts_file}