Merge bitcoin/bitcoin#34169: fuzz: change fuzz runner test_runner.py to be cwd independent

77c9b3c change test_runner.py to be cwd independent by calling subprocess.run with cwd arg. (Robin David)

Pull request description:

  Dear Maintainers,

  While using `test_runner.py` that runs fuzz tests and produces coverage results I encountered the following error.

  If not running the script from the project root directory the `git grep --function-context [...]` does not return the same output which results in the following Python error:

  ```
  ../../src/protocol.h-', '../../../src/protocol.h-/** nServices flags */']
  Traceback (most recent call last):
    File "/path/to/bitcoin/build_libfuzzer/test/fuzz/./test_runner.py", line 405, in <module>
      main()
      ~~~~^^
    File "/path/to/bitcoin/build_libfuzzer/test/fuzz/./test_runner.py", line 173, in main
      return generate_corpus(
          fuzz_pool=fuzz_pool,
      ...<3 lines>...
          targets=test_list_selection,
      )
    File "/path/to/bitcoin/build_libfuzzer/test/fuzz/./test_runner.py", line 249, in generate_corpus
      targets = transform_process_message_target(targets, Path(src_dir))
    File "/path/to/build_libfuzzer/test/fuzz/./test_runner.py", line 218, in transform_process_message_target
      assert len(lines)
             ~~~^^^^^^^
  AssertionError
  ```

  The script is not able to retrieve lines as the filter applied is:

  ```python
  lines = [l.split("::", 1)[1].split(",")[0].lower() for l in lines if l.startswith("src/protocol.h-    NetMsgType::")]
  ```

  Which when running from the root directory returns:
  ```
  [snip]
  src/protocol.h-    NetMsgType::VERSION,
  [snip]
  ```
  but returns a relative path to CWD when run from other directories e.g:
  ```
  ../../../src/protocol.h-    NetMsgType::VERSION,
  ```

  This is very unfortunate as the script rightfully read the `config.ini` relatively to itself and go fetch `BUILDDIR` and `SRCDIR`  variables to obtain absolute paths.

  Options are:
  * enforce running the script from *bitcoin/* directory  (and thus explicitly mentioning it in the doc)
  * make the script independent from where it is being run

  I chose the second option as it was fairly easy to make the script independent from where it is being run.

ACKs for top commit:
  maflcko:
    lgtm ACK 77c9b3c
  dergoegge:
    Code review ACK 77c9b3c

Tree-SHA512: fbc821c4790dd9ac125046a842498e0d9a48549d1c8ef150bce2193ee62bee9c3bfd4b17ce278411102dd200dc9ad86a176ecae29ca1667bb14d6f90ad67e01d

Author: fanquake

test/fuzz/test_runner.py

@@ -208,10 +208,11 @@ def transform_process_message_target(targets, src_dir):
     p2p_msg_target = "process_message"
     if (p2p_msg_target, {}) in targets:
         lines = subprocess.run(
-            ["git", "grep", "--function-context", "ALL_NET_MESSAGE_TYPES{", src_dir / "src" / "protocol.h"],
+            ["git", "grep", "--function-context", "ALL_NET_MESSAGE_TYPES{", "src/protocol.h"],
             check=True,
             stdout=subprocess.PIPE,
             text=True,
+            cwd=src_dir,
         ).stdout.splitlines()
         lines = [l.split("::", 1)[1].split(",")[0].lower() for l in lines if l.startswith("src/protocol.h-    NetMsgType::")]
         assert len(lines)
@@ -226,10 +227,11 @@ def transform_rpc_target(targets, src_dir):
     rpc_target = "rpc"
     if (rpc_target, {}) in targets:
         lines = subprocess.run(
-            ["git", "grep", "--function-context", "RPC_COMMANDS_SAFE_FOR_FUZZING{", src_dir / "src" / "test" / "fuzz" / "rpc.cpp"],
+            ["git", "grep", "--function-context", "RPC_COMMANDS_SAFE_FOR_FUZZING{", "src/test/fuzz/rpc.cpp"],
             check=True,
             stdout=subprocess.PIPE,
             text=True,
+            cwd=src_dir,
         ).stdout.splitlines()
         lines = [l.split("\"", 1)[1].split("\"")[0] for l in lines if l.startswith("src/test/fuzz/rpc.cpp-    \"")]
         assert len(lines)