Cortex-M backend: Fuse Relu, Hardtanh and Hardsigmoid

[AdrianLundell]

Implements a new pass which fuses activation passes with preceeding cortex-m ops if possible.

Removed quantization of conv1d, conv3d as they are not tested

• moves Conv+relu test to test_activations.

Propagate qmin, qmax to conv kernel.

cc @freddan80 @per @zingo @oscarandersson8218 @digantdesai

[pytorch-bot]

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✅ You can merge normally! (2 Unrelated Failures)

As of commit 9436522 with merge base 213d24c ():

BROKEN TRUNK - The following jobs failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• pull / unittest / linux / linux-job (gh) (trunk failure)
  exir/backend/test/test_lowered_backend_module.py::TestBackendAPI::test_emit_nested_lowered_backend_module
• pull / unittest-editable / linux / linux-job (gh) (trunk failure)
  exir/backend/test/test_lowered_backend_module.py::TestBackendAPI::test_emit_nested_lowered_backend_module

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