Add event tracing and ETDumps to executor_runner (#5027)

* Add event tracing and ETDumps to executor_runner

- Enabled via EXECUTORCH_ENABLE_EVENT_TRACER
- Add flag 'etdump_path' to specify the file path for the ETDump file
- Add flag 'num_executions' for number of iterations to run
- Create and pass event tracer 'ETDumpGen'
- Save ETDump to disk
- Update docs to reflect the changes

Signed-off-by: Benjamin Klimczak <benjamin.klimczak@arm.com>
Change-Id: I7e8e8b7f21453bb8d88fa2b9c2ef66c532f3ea46

* Fix comments during code review

- Raise a CMake error if event tracing is enabled without the devtools
- Re-factoring of the changes in the portable executor_runner
- Minor fix in docs

Change-Id: Ia50fef8172f678f9cbe2b33e2178780ff983f335
Signed-off-by: Benjamin Klimczak <benjamin.klimczak@arm.com>

* Small fix for use of flag `FLAGS_etdump`

Change-Id: I0ebb22636cdd64aea24bcee51cba05496ed78b1f

* Another fix for case ET_EVENT_TRACER_ENABLED=OFF

Change-Id: I7d72e4d8f46ec727a60c9553851d5b71da8e91d4
Signed-off-by: Benjamin Klimczak <benjamin.klimczak@arm.com>

* Revert use of FLATCCRT_LIB to flatccrt

Signed-off-by: Benjamin Klimczak <benjamin.klimczak@arm.com>
Change-Id: I5e7d8ef5d66bc3d5de36ea451b31fb3bdcd42d09

* Fix linker issue when building executor_runner

- Remove explicit addition of `-DET_EVENT_TRACER_ENABLED` from
  backends/qualcomm/CMakeLists.txt as setting the definition without
  enabling cmake flag `EXECUTORCH_ENABLE_EVENT_TRACER` caused issues
  when building the executor_runner.
- Replace deprecated namespace `torch::executor` with
  `executorch::etdump` in the executor_runner.cpp.

Signed-off-by: Benjamin Klimczak <benjamin.klimczak@arm.com>
Change-Id: Iadff38374e661f42e394dc69903548922ca08aea

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Signed-off-by: Benjamin Klimczak <benjamin.klimczak@arm.com>