Move user-defined passes after SpecPropPass

[lucylq]

Summary:

1. Use ExecutorchBackendConfig instead of inserting the pass.
2. Move SpecPropPass after user-defined passes. It was originally swapped here: D80840528. cc ethansfng, who has a pass that should run before SpecPropPass

Differential Revision: D87576772

[pytorch-bot]

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[meta-codesync]

@lucylq has exported this pull request. If you are a Meta employee, you can view the originating Diff in D87576772.

[meta-codesync]

@lucylq has exported this pull request. If you are a Meta employee, you can view the originating Diff in D87576772.

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[JacobSzwejbka]

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