cmake : add install() for impl libraries + fix apple builds (#23511)

* pi : update

* ci : fix ios build

* ci : fix andoroid

* ci : fix apple builds

* cmake : add install() for impl libraries

Add install(TARGETS <target> LIBRARY) for all -impl libraries that were
changed from STATIC to shared (controlled by BUILD_SHARED_LIBS) in
commit bb28c1fe2. Without this, cmake --install fails to copy the shared
libraries, causing runtime errors like:

  llama-server: error while loading shared libraries: libllama-server-impl.so

Ref: https://github.com/ggml-org/llama.cpp/issues/23494#issuecomment-4512912515

Assisted-by: llama.cpp:local pi

* ci : fix xcframework build

.github/workflows/release.yml

@@ -1108,6 +1108,7 @@ jobs:
             -DGGML_METAL_USE_BF16=ON \
             -DGGML_METAL_EMBED_LIBRARY=ON \
             -DLLAMA_OPENSSL=OFF \
+            -DLLAMA_BUILD_APP=OFF \
             -DLLAMA_BUILD_EXAMPLES=OFF \
             -DLLAMA_BUILD_TOOLS=OFF \
             -DLLAMA_BUILD_TESTS=OFF \