flake8: fix nested import checks

Import modules at the top of the module in most cases.  Many of these
weren't actually saving any time:
* editor: shlex is already imported by the main module
* platform_utils: On Windows, the win32 module is almost always needed
* tests: There's no point in optimizing these.

The trace import in the main module is about the only one worth allowing
since that module itself is rarely used, and only when in a specific
debug mode.

Change-Id: I5d3fcecbe51e0ce78d4e856d7033565150ef4526
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/654103
Commit-Queue: Mike Frysinger <vapier@google.com>
Reviewed-by: Brian Gan <brgan@google.com>
Tested-by: Mike Frysinger <vapier@google.com>

tests/test_subcmds.py

@@ -21,6 +21,7 @@ import pytest
 
 from command import Command
 import subcmds
+from subcmds import sync
 
 
 # NB: We don't test all subcommands as we want to avoid "change detection"
@@ -164,9 +165,7 @@ def test_common_validate_options(name: str, cls: Type[Command]) -> None:
 
 def test_attribute_error_repro() -> None:
     """Confirm that accessing verbose before CommonValidateOptions fails."""
-    from subcmds.sync import Sync
-
-    cmd = Sync()
+    cmd = sync.Sync()
     opts, args = cmd.OptionParser.parse_args([])
 
     # This confirms that without the fix in main.py, an AttributeError

tests/test_subcmds_sync.py

@@ -19,6 +19,7 @@ import optparse
 import os
 from pathlib import Path
 import shutil
+import subprocess
 import tempfile
 import threading
 import time
@@ -3012,8 +3013,6 @@ class TestSmartSyncSetupRemoteHelper(unittest.TestCase):
         self, mock_transport_class, mock_server_class, mock_popen, mock_which
     ):
         """Test _SmartSyncSetup when a helper is present and succeeds."""
-        import subprocess
-
         self.manifest.manifest_server = (
             "persistent-https://android-smartsync.corp.google.com/"
             "manifestserver"