Update build system for wxWidgets 3.1.5 → 3.3.2 upgrade

- deps/wxWidgets/wxWidgets.cmake: Add GIT_TAG v3.3.2 to track the
  correct branch; remove -DwxUSE_UNICODE=ON (unicode-only in 3.3,
  option removed)
- src/CMakeLists.txt: Bump find_package minimum version from 3.0/3.1
  to 3.3; remove SLIC3R_WX_STABLE conditional (3.0 no longer supported)
- CMakeLists.txt: Remove SLIC3R_WX_STABLE option definition
- scripts/flatpak/com.orcaslicer.OrcaSlicer.yml: Update wxWidgets
  source URL to v3.3.2 branch archive; remove sha256 (placeholder
  TODO); remove -DwxUSE_UNICODE=ON

deps/wxWidgets/wxWidgets.cmake

@@ -32,6 +32,7 @@ endif()
 orcaslicer_add_cmake_project(
     wxWidgets
     GIT_REPOSITORY "https://github.com/SoftFever/Orca-deps-wxWidgets"
+    GIT_TAG v3.3.2
     GIT_SHALLOW ON
     DEPENDS ${PNG_PKG} ${ZLIB_PKG} ${EXPAT_PKG} ${JPEG_PKG}
     CMAKE_ARGS
@@ -44,7 +45,6 @@ orcaslicer_add_cmake_project(
         ${_wx_shared}
         -DwxUSE_MEDIACTRL=ON
         -DwxUSE_DETECT_SM=OFF
-        -DwxUSE_UNICODE=ON
         -DwxUSE_PRIVATE_FONTS=ON
         -DwxUSE_OPENGL=ON
         -DwxUSE_GLCANVAS_EGL=OFF