cmake: build shared libexecutorch_quantized_ops when EXECUTORCH_BUILD_SHARED=ON

Create a single libexecutorch_quantized_ops.so that bundles
quantized_ops_lib and quantized_kernels, allowing consumers to link
quantized op implementations via a shared library.

quantized_ops_lib already has --whole-archive as an INTERFACE link
option from Codegen.cmake, so we do not wrap it in
$<LINK_LIBRARY:WHOLE_ARCHIVE,...> to avoid pulling the registration
constructor in twice. Link against executorch_shared (not
executorch_core) to share a single operator registry.

Co-authored-by: Claude <noreply@anthropic.com>

Author: tomeuv

kernels/quantized/CMakeLists.txt

@@ -157,3 +157,12 @@ install(
   PUBLIC_HEADER
     DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/executorch/kernels/quantized/
 )
+
+if(EXECUTORCH_BUILD_SHARED)
+  executorch_add_shared_library(
+    executorch_quantized_ops
+    quantized_ops_lib
+    quantized_kernels
+    executorch_shared
+  )
+endif()