Enably QtForPython for Linux (#5667)

- Fix PALification and include Linux for the QtForPython gem
- Add Linux-only module loader for Pyside2 related modules
- Remove (unnecessary) #if !defined(Q_OS_WIN)

Signed-off-by: Steve Pham <82231385+spham-amzn@users.noreply.github.com>

Gems/QtForPython/Code/CMakeLists.txt

@@ -21,7 +21,8 @@ ly_add_target(
     NAME QtForPython.Editor.Static STATIC
     NAMESPACE Gem
     FILES_CMAKE
-        qtforpython_editor_${PAL_PLATFORM_NAME_LOWERCASE}_files.cmake
+        qtforpython_editor_files.cmake
+        ${CMAKE_CURRENT_SOURCE_DIR}/Source/Platform/${PAL_PLATFORM_NAME}/qtforpython_editor_${PAL_PLATFORM_NAME_LOWERCASE}_files.cmake
     PLATFORM_INCLUDE_FILES
         ${common_source_dir}/${PAL_TRAIT_COMPILER_ID}/qtforpython_${PAL_TRAIT_COMPILER_ID_LOWERCASE}.cmake
     INCLUDE_DIRECTORIES
@@ -45,6 +46,9 @@ ly_add_target(
     NAMESPACE Gem
     FILES_CMAKE
         qtforpython_shared_files.cmake
+    INCLUDE_DIRECTORIES
+        PRIVATE
+            ${CMAKE_CURRENT_SOURCE_DIR}/Source/Platform/${PAL_PLATFORM_NAME}
     BUILD_DEPENDENCIES
         PRIVATE
             Gem::QtForPython.Editor.Static