Export lora weights to sep file

[pytorchbot]

This PR was created by the merge bot to help merge the original PR into the main branch.
ghstack PR number: #14756 by @lucylq
^ Please use this as the source of truth for the PR details, comments, and reviews
ghstack PR base: https://github.com/pytorch/executorch/tree/gh/lucylq/117/base
ghstack PR head: https://github.com/pytorch/executorch/tree/gh/lucylq/117/head
Merge bot PR base: https://github.com/pytorch/executorch/tree/gh/lucylq/119/orig
Merge bot PR head: https://github.com/pytorch/executorch/tree/gh/lucylq/117/orig
Differential Revision: D83777195
@diff-train-skip-merge

[pytorch-bot]

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❌ 5 New Failures, 37 Pending

As of commit fa17199 with merge base 2eb8994 ():

NEW FAILURES - The following jobs have failed:

• pull / test-qnn-wheel-packages-linux (3.10) / linux-job (gh)
  RuntimeError: Command docker exec -t e1db6e372fc10bf9a0a812b0c24fc1cf568ac30be803683ccc40f991c0c9e585 /exec failed with exit code 1
• pull / test-qnn-wheel-packages-linux (3.11) / linux-job (gh)
  RuntimeError: Command docker exec -t c1443da7a155546b7ace3fb5d4b5980d2ca0245ab4e8c2bd584ea7d773e2ee09 /exec failed with exit code 1
• pull / test-qnn-wheel-packages-linux (3.12) / linux-job (gh)
  RuntimeError: Command docker exec -t 6d601099506495331ea4b8a95a0a9894b5ba6e6cc8fa5c09346c132747fac52c /exec failed with exit code 1
• pull / unittest / linux / linux-job (gh)
  backends/xnnpack/test/passes/test_channels_last_tagged_reshape.py::TestChannelsLastTaggedReshapePass::test_q_dq_nodes_around_copy_are_tagged
• trunk / test-arm-cortex-m-size-test (zephyr-preset) / linux-job (gh)
  RuntimeError: Command docker exec -t 36cfc62f663584c48ad4eea001163d451bf31478327f3deac43ca98162db9682 /exec failed with exit code 1

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