[MPS Delegate] Add new mps runtime with support for FP16, lifted and unlifted graphs (iOS15+, macOS12+)

[DenisVieriu97]

This PR changes the MPS Backend runtime to support for iOS15+/macOS12+ (previous runtime was limited to iOS17/macOS14 only). Additionally, this PR contains changes such as support for both lifted and unlifted graphs, support for torch.export API, optimizations for FP16 and faster model loading during runtime (more information in the summary).

Summary of changes:

• Add support for running the models in FP16 (https://github.com/DenisVieriu97/executorch/pull/7 @georgepaw)
• Replace the previous MPS runtime from ExecuTorch which was relying on iOS17 / macOS Sonoma APIs for serialization of the MPSGraphExecutable. Instead of creating the MPSGraph nodes and serializing them during AOT, create the corresponding entries of the EdgeIR nodes in the FlatBuffer, and parse them during runtime to construct the graph. This removes any dependency on iOS17 / macOS 14.0 APIs.
• Add support for node visitor pattern:
  • Each node visitor class visits an op and serializes the data into MPSTensors and MPSNodes which get appended in the flatbuffer
  • The entries from the FlatBuffer are parsed in the runtime and based on them the MPSGraph is constructed (for more info see MPSGraphBuilder class and corresponding ops from operators/ folder.
  • This method removes the additional read and writes to disk of the MPSGraphExecutable (once during AOT and once during runtime).

Models summary:

Model	FP16	FP32
mul
add_mul
linear
edsr
Mobilebert
mv2
mv3
vit
w2l
ic3
ic4
resnet18
resnet50
Llama2
emformer_join
emformer_predict
emformer_transcribe
dl3

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/1655

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✅ You can merge normally! (1 Unrelated Failure)

As of commit 8d94299 with merge base 93dd96f ():

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

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

• Lint / lintrunner / linux-job (gh)
  >>> Lint for extension/pybindings/test/make_test.py:

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@shoumikhin merged this pull request in cbc0c95.