pico2: link executorch_core after kernel libs to fix --whole-archive resolution (#19163)

### Summary

The Pico2 firmware link fails with an undefined reference to
BoxedEvalueList<std::optional<Tensor>>::get() from
RegisterCodegenUnboxedKernelsEverything.cpp.obj inside
libportable_ops_lib.a. ld walks the link line once: by the time
--whole-archive pulls the codegen TU's reference into the link,
libexecutorch_core.a (which contains the evalue.cpp specialization) has
already been processed.

Pico2 was green until #18962 (TOB-EXECUTORCH-31 fix), which removed
EValue::~EValue's inline call to BoxedEvalueList::get(). Before that
commit, libexecutorch_core.a had its own use of the symbol that forced
evalue.cpp.o to be pulled early; the link-order bug was always latent
and the destructor change unmasked it.

Move libexecutorch_core.a to after the kernel archives in all four
USE_CMSIS_NN x USE_SELECTIVE_BUILD branches so the codegen TUs can still
resolve their references after --whole-archive.

Authored with Claude.

### Test plan
CI

Author: rascani

examples/raspberry_pi/pico2/CMakeLists.txt

@@ -144,31 +144,35 @@ if(USE_CMSIS_NN)
     # CMSIS-NN model uses only cortex_m:: ops, no portable ops needed. Skip
     # --whole-archive on portable_ops_lib to avoid pulling unused ops.
     message(STATUS "Selective build: CMSIS-NN only (no portable ops)")
+    # libexecutorch_core.a is listed after the kernel libs so that any
+    # references introduced by --whole-archive (e.g. EValue accessors used by
+    # the codegen-generated kernel registrations) can still pull in symbols from
+    # evalue.cpp. ld walks the link line once, left to right.
     target_link_libraries(
       executorch_pico
       PRIVATE ${BAREMETAL_BUILD_DIR}/lib/libexecutorch.a
-              ${BAREMETAL_BUILD_DIR}/lib/libexecutorch_core.a
               -Wl,--whole-archive
               ${BAREMETAL_BUILD_DIR}/lib/libcortex_m_ops_lib.a
               -Wl,--no-whole-archive
               ${BAREMETAL_BUILD_DIR}/lib/libcortex_m_kernels.a
               ${BAREMETAL_BUILD_DIR}/lib/libportable_kernels.a
               ${BAREMETAL_BUILD_DIR}/lib/libcmsis-nn.a
+              ${BAREMETAL_BUILD_DIR}/lib/libexecutorch_core.a
               pico_stdlib
               pico_stdio_usb
     )
   else()
     target_link_libraries(
       executorch_pico
       PRIVATE ${BAREMETAL_BUILD_DIR}/lib/libexecutorch.a
-              ${BAREMETAL_BUILD_DIR}/lib/libexecutorch_core.a
               -Wl,--whole-archive
               ${BAREMETAL_BUILD_DIR}/lib/libcortex_m_ops_lib.a
               ${BAREMETAL_BUILD_DIR}/lib/libportable_ops_lib.a
               -Wl,--no-whole-archive
               ${BAREMETAL_BUILD_DIR}/lib/libcortex_m_kernels.a
               ${BAREMETAL_BUILD_DIR}/lib/libportable_kernels.a
               ${BAREMETAL_BUILD_DIR}/lib/libcmsis-nn.a
+              ${BAREMETAL_BUILD_DIR}/lib/libexecutorch_core.a
               pico_stdlib
               pico_stdio_usb
     )
@@ -179,23 +183,23 @@ else()
     target_link_libraries(
       executorch_pico
       PRIVATE ${BAREMETAL_BUILD_DIR}/lib/libexecutorch.a
-              ${BAREMETAL_BUILD_DIR}/lib/libexecutorch_core.a
               -Wl,--whole-archive
               ${BAREMETAL_BUILD_DIR}/lib/libexecutorch_selected_kernels.a
               -Wl,--no-whole-archive
               ${BAREMETAL_BUILD_DIR}/lib/libportable_kernels.a
+              ${BAREMETAL_BUILD_DIR}/lib/libexecutorch_core.a
               pico_stdlib
               pico_stdio_usb
     )
   else()
     target_link_libraries(
       executorch_pico
       PRIVATE ${BAREMETAL_BUILD_DIR}/lib/libexecutorch.a
-              ${BAREMETAL_BUILD_DIR}/lib/libexecutorch_core.a
               -Wl,--whole-archive
               ${BAREMETAL_BUILD_DIR}/lib/libportable_ops_lib.a
               -Wl,--no-whole-archive
               ${BAREMETAL_BUILD_DIR}/lib/libportable_kernels.a
+              ${BAREMETAL_BUILD_DIR}/lib/libexecutorch_core.a
               pico_stdlib
               pico_stdio_usb
     )