[CMake] Avoid extension_module have dupe flat_tensor cpp

Currently, _extension_module__srcs has srcs from flat_tensor. This is
bad.

```
set(_extension_module__srcs
    extension/flat_tensor/flat_tensor_data_map.cpp
    extension/flat_tensor/serialize/flat_tensor_header.cpp
    extension/module/module.cpp
)
```

We need to update deps. We need to export extension_flat_tensor to
install directory.

Author: kirklandsign

extension/android/CMakeLists.txt

@@ -72,6 +72,7 @@ list(
   link_libraries
   executorch
   extension_data_loader
+  extension_flat_tensor
   extension_module
   extension_runner_util
   extension_tensor

extension/flat_tensor/CMakeLists.txt

@@ -18,7 +18,7 @@ endif()
 
 list(TRANSFORM _extension_flat_tensor__srcs PREPEND "${EXECUTORCH_ROOT}/")
 add_library(extension_flat_tensor ${_extension_flat_tensor__srcs})
-target_link_libraries(extension_flat_tensor executorch extension_data_loader)
+target_link_libraries(extension_flat_tensor executorch_core)
 target_include_directories(
   extension_flat_tensor
   PUBLIC ${EXECUTORCH_ROOT}/..

tools/cmake/cmake_deps.toml

@@ -198,7 +198,6 @@ filters = [
 deps = [
   "extension_flat_tensor_schema",
   "executorch_core",
-  "executorch",
 ]
 
 [targets.extension_module]
@@ -209,9 +208,9 @@ filters = [
   ".cpp$",
 ]
 deps = [
-  "executorch",
   "executorch_core",
   "extension_data_loader",
+  "extension_flat_tensor",
 ]
 
 [targets.extension_runner_util]

tools/cmake/executorch-config.cmake

@@ -66,6 +66,7 @@ set(lib_list
     etdump
     bundled_program
     extension_data_loader
+    extension_flat_tensor
     ${FLATCCRT_LIB}
     coreml_util
     coreml_inmemoryfs