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	2023-03-23 15:00:31.000000000 +0100
+++ b/src/linguist/Qt5LinguistToolsMacros.cmake	2023-05-19 23:42:31.618949027 +0000
@@ -68,6 +68,7 @@
     if(NOT EXISTS "${stamp_file_dir}")
         file(MAKE_DIRECTORY "${stamp_file_dir}")
     endif()
+    set(stamp_files "")
     foreach(_ts_file ${_my_tsfiles})
         get_filename_component(_ts_name ${_ts_file} NAME)
         if(_my_sources)
@@ -95,7 +96,14 @@
 
           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")
+        list(APPEND stamp_files ${stamp_file})
+        get_filename_component(full_stamp_file_dir "${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}
@@ -103,7 +111,7 @@
             DEPENDS ${_dependencies}
             VERBATIM)
     endforeach()
-    qt5_add_translation(${_qm_files} __QT_INTERNAL_DEPEND_ON_TIMESTAMP_FILE ${_my_tsfiles})
+    qt5_add_translation(${_qm_files} ${_my_tsfiles} __QT_INTERNAL_TIMESTAMP_FILES ${stamp_files})
     set(${_qm_files} ${${_qm_files}} PARENT_SCOPE)
 endfunction()
 
@@ -120,17 +128,17 @@
 
 
 function(QT5_ADD_TRANSLATION _qm_files)
-    set(options __QT_INTERNAL_DEPEND_ON_TIMESTAMP_FILE)
+    set(options)
     set(oneValueArgs)
-    set(multiValueArgs OPTIONS)
+    set(multiValueArgs OPTIONS __QT_INTERNAL_TIMESTAMP_FILES)
 
     cmake_parse_arguments(_LRELEASE "${options}" "${oneValueArgs}" "${multiValueArgs}" ${ARGN})
     set(_lrelease_files ${_LRELEASE_UNPARSED_ARGUMENTS})
 
+    set(idx 0)
     foreach(_current_FILE ${_lrelease_files})
         get_filename_component(_abs_FILE ${_current_FILE} ABSOLUTE)
         get_filename_component(qm ${_abs_FILE} NAME)
-        set(ts_stamp_file "${CMAKE_CURRENT_BINARY_DIR}/.lupdate/${qm}.stamp")
         # everything before the last dot has to be considered the file name (including other dots)
         string(REGEX REPLACE "\\.[^.]*$" "" FILE_NAME ${qm})
         get_source_file_property(output_location ${_abs_FILE} OUTPUT_LOCATION)
@@ -141,7 +149,9 @@
             set(qm "${CMAKE_CURRENT_BINARY_DIR}/${FILE_NAME}.qm")
         endif()
 
-        if(_LRELEASE___QT_INTERNAL_DEPEND_ON_TIMESTAMP_FILE)
+        if(_LRELEASE___QT_INTERNAL_TIMESTAMP_FILES)
+            list(GET _LRELEASE___QT_INTERNAL_TIMESTAMP_FILES ${idx} ts_stamp_file)
+            math(EXPR idx "${idx} + 1")
             set(qm_dep "${ts_stamp_file}")
         else()
             set(qm_dep "${_abs_FILE}")