build: raise cmake_minimum_required to 3.5 for CMake 4.x compatibility

[Code-0-0]

Summary

CMake 4.0 removed compatibility with cmake_minimum_required(VERSION < 3.5) and now aborts the
configure step with:

CMake Error at CMakeLists.txt:1 (cmake_minimum_required):
  Compatibility with CMake < 3.5 has been removed from CMake.
  Update the VERSION argument <min> value.  Or, use the <min>...<max> syntax ...
  Or, add -DCMAKE_POLICY_VERSION_MINIMUM=3.5 to try configuring anyway.

core/src/main/cpp/CMakeLists.txt still requests VERSION 3.0, so any local build that ends up
using a CMake >= 4.0 (for example the CMake shipped with a MinGW/MSYS2 toolchain, or a CMake
selected through cmake.dir in local.properties) fails before anything is compiled. CI is not
affected because it uses the SDK's CMake 3.22.1 — which accepts 3.5 just as well.

Change

-cmake_minimum_required(VERSION 3.0)
+# 3.5 is the minimum accepted by CMake 4.x (anything lower is a hard error there)
+cmake_minimum_required(VERSION 3.5)

Nothing in this file depends on policies introduced after 3.5 (execute_process, configure_file,
string(TIMESTAMP), list(GET), add_library, target_link_libraries), so the bump only widens
the accepted range at the top: CMake 4.x works, and CMake >= 3.5 keeps working.

(If touching this file is undesirable, the equivalent workaround is to pass
-DCMAKE_POLICY_VERSION_MINIMUM=3.5 from core/build.gradle.kts's externalNativeBuild.cmake
arguments.)

Verification

The same change was part of a fork build of app:assembleAlphaRelease on the Build Debug
workflow (which uses the SDK CMake 3.22.1), and the native bridge target configured and linked
successfully, all four ABIs:
https://github.com/Code-0-0/ClashMetaForAndroid/actions/runs/35441174195