Use builtin harfbuzz to workaround GDExtension crash

[j20001970]

Since godotengine/godot#100052 is merged in v4.4, we can now configure linux dependency modules independently.

Currently Godot has a bug (godotengine/godot#91401) that if the engine is using system-provided harfbuzz library, it will crash when GDExtension libraries call std::call_once during static initialization. Libraries with such pattern are including but not limited to Tensorflow/Protobuf-based projects, GDExtension libraries with these dependencies will always crash flatpak Godot unless builtin harfbuzz is used.

This PR remove the builtin_harfbuzz=no from Scons flags, making the editor to use builtin harfbuzz instead of system-provided one from Freedesktop SDK/Platform. The editor executable size increase in my testing is from 139.2 MiB (145,966,624) to 139.9 MiB (146,660,800) which is acceptable at the scale of flatpak apps IMO.

[flathubbot]

Started test build 184476

[flathubbot]

Build 184476 successful
To test this build, install it from the testing repository:

flatpak install --user https://dl.flathub.org/build-repo/167702/org.godotengine.Godot.flatpakref

[Calinou]

Thanks!