Fix ConvertMmToBmmPass for quantized (int8/int16) mm ops (#18974)

[apullin]

Summary:

This diff is experimental, but appears to address incomplete support for INT pathways for BMM. TBD.

The pass converts rank-2 mm to rank-3 bmm (required by TOSA spec) via
unsqueeze/bmm/squeeze. Previously it called super().call() to re-trace
the graph on FakeTensors for shape propagation, but aten.bmm rejects
int8/int16 FakeTensors, causing failures for any quantized mm ops.

Since mm→bmm is a pure shape transformation (adding a batch dim of 1),
we can set the output metadata directly: unsqueeze the mm's FakeTensor
for the bmm node, and use the original for the squeeze. No need to
re-execute the op.

Reviewed By: digantdesai

Differential Revision: D99857137

[pytorch-bot]

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[meta-codesync]

@apullin has exported this pull request. If you are a Meta employee, you can view the originating Diff in D99857137.

[digantdesai]

Review automatically exported from Phabricator review in Meta.

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