Cortex-M backend: Improve int8-portable operator support

[AdrianLundell]

Using the int8 portable ops is an option for most ops not requiring rescales such as data move ops, max/min ops and logic ops. Even though they are not accelerated, quantizing them to int8 is more efficient than doing them in fp32+dequant/quantization.

This patch adds a large number of such ops to be quantized by the SharedQspecQuantizer together with tests. It also modifies the quantizer to increase the support:

• If multiple qspecs are found, use top one rather than falling back to fp32 since this is what users most likely want.
• Reject node with non-float inputs/outputs which would previously crash
• Let BFS algorithm search through non-float edges to support indexing ops.

cc @digantdesai @SS-JIA @freddan80 @per @zingo @oscarandersson8218 @mansnils @Sebastian-Larsson @robell

[pytorch-bot]

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❌ 1 Awaiting Approval, 3 New Failures

As of commit 3771a54 with merge base dae7a02 ():

AWAITING APPROVAL - The following workflow needs approval before CI can run:

• periodic (gh)

NEW FAILURES - The following jobs have failed:

• pull / test-samsung-models-linux / linux-job (gh)
  RuntimeError: Command docker exec -t f3135b9c72550e156eea4aed1d917a23bef85d5da65f1a03a8eb34b6ad4b7343 /exec failed with exit code 1
• pull / test-samsung-quantmodels-linux / linux-job (gh)
  RuntimeError: Command docker exec -t 81d9b0d1993013361fcc6513b10f8eee0a72e6cb0e3f684497ca5256ac6ef897 /exec failed with exit code 1
• trunk / test-arm-backend-vkml (test_pytest_ops_vkml) / linux-job (gh)
  RuntimeError: Command docker exec -t 93bb80811a5c4ed585393f615df07eafab00ec516aea70ab4f8022dc43a8f796 /exec failed with exit code 1

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[AdrianLundell]

Unrelated fails