[wasm] Fix inclusion of `marshal-ilgen` component (#87629)

[wasm] Fix inclusion of `marshal-ilgen` component (#87629)

* [wasm] Fix inclusion of `marshal-ilgen`

Issue: `marshal-ilgen` component never included

Reason:
The item inclusion was being done *outside* any targets, which would get
evaluated *before* any targets are run.

But the item that it depends on to decide whether to include
`marshal-ilgen` is in target
`_ScanAssembliesDecideLightweightMarshaler`.

This broke microbenchmarks with:
```
Error: [MONO] * Assertion at /__w/1/s/src/mono/mono/component/marshal-ilgen-stub.c:28, condition `!m_type_is_byref(t)' not met

    at ft (/home/helixbot/work/96640802/w/B9C40A15/e/performance/artifacts/bin/for-running/MicroBenchmarks/fa21f9df-08d0-43a4-b28d-0078821ea492/bin/net8.0/browser-wasm/AppBundle/dotnet.runtime.js:3:12422)
    at mt (/home/helixbot/work/96640802/w/B9C40A15/e/performance/artifacts/bin/for-running/MicroBenchmarks/fa21f9df-08d0-43a4-b28d-0078821ea492/bin/net8.0/browser-wasm/AppBundle/dotnet.runtime.js:3:12676)
    at wasm_trace_logger (wasm://wasm/00a5f7d6:wasm-function[7879]:0x1e41d0)
    at eglib_log_adapter (wasm://wasm/00a5f7d6:wasm-function[581]:0x37fbb)
    at monoeg_g_logv_nofree (wasm://wasm/00a5f7d6:wasm-function[504]:0x35f57)
    at monoeg_assertion_message (wasm://wasm/00a5f7d6:wasm-function[508]:0x36078)
    at mono_assertion_message (wasm://wasm/00a5f7d6:wasm-function[510]:0x360bb)
    at stub_emit_marshal_ilgen (wasm://wasm/00a5f7d6:wasm-function[1300]:0x66db1)
    at mono_emit_marshal (wasm://wasm/00a5f7d6:wasm-function[1820]:0x8990b)
    at emit_native_wrapper_ilgen (wasm://wasm/00a5f7d6:wasm-function[2651]:0xb86de)
```

* [wasm] WBT: Use sdk 8.0.100-preview.6.23314.19

.. to workaround https://github.com/dotnet/runtime/issues/87647 .

* [wasm] Add test for marshal-ilgen - wbt

* add missing file