Recipe and Input class definitions with e2e export (#10034)

Based on the discussion in
#9027

This PR adds the executorch.export API and all the supporting components
required for it. At a high level the executorch.export API takes in a
model, example inputs and a recipe, then underneath the hood executes
all the steps required to export, quantize and lower the model based on
the recipe.

The pipeline consists of a staged setup where each major step in the
process such as Export, Quantization etc. is listed as a separate stage
and a chain of these is formed and then executed. The result of this
will be that we'll get a PTE file which can then be executed on device.

The major new components added in this PR are:
- class definition for ExportSession and ExportRecipe
- Definitions for each stage in the process
- executorch.export API which will return a session object that the user
can then use to get access to the PTE file, run the model via
pybindings, print delegation info etc.

Author: tarun292

export/TARGETS

@@ -0,0 +1,38 @@
+load("@fbcode_macros//build_defs:python_library.bzl", "python_library")
+
+oncall("executorch")
+
+python_library(
+    name = "recipe",
+    srcs = [
+        "recipe.py",
+    ],
+    deps = [
+        "//caffe2:torch",
+        "//executorch/exir/backend:backend_api",
+        "//executorch/exir:pass_manager",
+        "//executorch/devtools/backend_debug:delegation_info",
+    ]
+)
+
+python_library(
+    name = "export",
+    srcs = [
+        "export.py",
+    ],
+    deps = [
+        ":recipe",
+        "//executorch/runtime:runtime",
+    ]
+)
+
+python_library(
+    name = "lib",
+    srcs = [
+        "__init__.py",
+    ],
+    deps = [
+        ":export",
+        ":recipe",
+    ],
+)

export/__init__.py

@@ -0,0 +1,24 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the BSD-style license found in the
+# LICENSE file in the root directory of this source tree.
+
+"""
+ExecuTorch export module.
+
+This module provides the tools and utilities for exporting PyTorch models
+to the ExecuTorch format, including configuration, quantization, and
+export management.
+"""
+
+# pyre-strict
+
+from .export import export, ExportSession
+from .recipe import ExportRecipe
+
+__all__ = [
+    "ExportRecipe",
+    "ExportSession",
+    "export",
+]