Arm backend: Add devtools support to example

[zingo]

New flags on run.sh --etdump Build in etdump and profiling, the etdump base64 coded and put in the log --debug_build Build debug instead of release --extra_build_flags Extra flags to pass to cmake this makes it for example possible to override the allocator pool size or other build time cmake flags.

The devtools build has been updated so FLATCC_EXECUTABLE can be used to point out the executable as seem to be intended to be possible but was not working.

[pytorch-bot[bot]]

:link: Helpful Links

:test_tube: See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/6959

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As of commit ed1bdd732e45b128fce5580fb4de00c0aab582ee with merge base 43555d21c289669ecacca5cd46d9a9018c6d7f7c (): :green_heart: Looks good so far! There are no failures yet. :green_heart:

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[zingo]

@pytorchbot label "topic: not user facing"

[zingo]

@digantdesai This changes files outside Arm folders and need a review from you, Thanks for your time!