mono#19535)

* [wasm][debugger] Show signature for delegate, or target, if available (mono#19505)

* [wasm][debugger] Show signature for delegate, or target, if available

- As object properties, we return a `Target` which has the signature of
the delegate target.

Fixes mono#19382

* [wasm][debugger] Some tidying up

* [wasm][debugger] Remove unused `sig_desc`

* [wasm][debugger] Simplify code, avoid extra allocations

.. as suggested by @lewing

(cherry picked from commit 4eca12e)

* [wasm][debugger] Fix tests broken because unused vars are not null

.. anymore, which is because we disabled optimizations in the
interpreter when debugging.

* [wasm][debugger][tests] Add tests to also check delegates in previous

.. frames.

* [wasm][debugger] Disable a test that tried to look at previous async

.. frames. This just happened to work. Currently, the trace has details
of the async machinery, instead of one reflecting what it might have
looked like for a non-async case. So, we can't reliably find the
previous method to inspect it's locals.

* [wasm][debugger] Fix test