[build Folder Migration] Move buck scripts for cmake (#9336)

### Summary

A series of diffs as a part of
#9117.

### Test plan

CI

```
$ rm -rf pip-out && python setup.py bdist_wheel
```


cc @larryliu0820 @lucylq

Author: jathu

tools/__init__.py

@@ -218,8 +218,8 @@ function(extract_sources sources_file)
     endif()
     execute_process(
       COMMAND
-        ${PYTHON_EXECUTABLE} ${executorch_root}/build/extract_sources.py
-        --config=${executorch_root}/build/cmake_deps.toml --out=${sources_file}
+        ${PYTHON_EXECUTABLE} ${executorch_root}/tools/cmake/extract_sources.py
+        --config=${executorch_root}/tools/cmake/cmake_deps.toml --out=${sources_file}
         --buck2=${BUCK2} ${target_platforms_arg}
       OUTPUT_VARIABLE gen_srcs_output
       ERROR_VARIABLE gen_srcs_error
@@ -254,7 +254,7 @@ function(resolve_buck2)
   endif()
 
   set(resolve_buck2_command
-      ${PYTHON_EXECUTABLE} ${executorch_root}/build/resolve_buck.py
+      ${PYTHON_EXECUTABLE} ${executorch_root}/tools/cmake/resolve_buck.py
       --cache_dir=buck2-bin
   )
 

tools/cmake/Utils.cmake

@@ -8,12 +8,20 @@
 import os
 import subprocess
 import sys
+from functools import cache
+from pathlib import Path
 
 from typing import Optional, Sequence
 
 
-# Run buck2 from the same directory (and thus repo) as this script.
-BUCK_CWD: str = os.path.dirname(os.path.realpath(__file__))
+@cache
+def repo_root_dir() -> Path:
+    git_root = subprocess.check_output(
+        ["git", "rev-parse", "--show-toplevel"],
+        cwd=os.path.dirname(os.path.realpath(__file__)),
+        text=True,
+    ).strip()
+    return Path(git_root)
 
 
 class Buck2Runner:
@@ -26,7 +34,7 @@ def run(self, args: Sequence[str]) -> list[str]:
             cp: subprocess.CompletedProcess = subprocess.run(
                 [self._path] + args,  # type: ignore[operator]
                 capture_output=True,
-                cwd=BUCK_CWD,
+                cwd=repo_root_dir(),
                 check=True,
             )
             return [line.strip().decode("utf-8") for line in cp.stdout.splitlines()]

tools/cmake/__init__.py

@@ -37,10 +37,10 @@
 
 """
 
+
 # Path to the file containing BUCK2 version (build date) for ExecuTorch.
-# Note that this path is relative to this script file, not the working
-# directory.
-BUCK_VERSION_FILE = "../.ci/docker/ci_commit_pins/buck2.txt"
+def _buck_version_path() -> Path:
+    return buck_util.repo_root_dir() / ".ci/docker/ci_commit_pins/buck2.txt"
 
 
 @dataclass
@@ -125,9 +125,7 @@ def resolve_buck2(args: argparse.Namespace) -> Union[str, int]:
 
     # Read the target version (build date) from the CI pin file. Note that
     # this path is resolved relative to the directory containing this script.
-    script_dir = os.path.dirname(__file__)
-    version_file_path = Path(script_dir) / BUCK_VERSION_FILE
-    with open(version_file_path.absolute().as_posix()) as f:
+    with open(_buck_version_path().absolute().as_posix()) as f:
         target_buck_version = f.read().strip()
 
     # Determine the target buck2 version string according to the current