PY-86985: Do not automatically mark source root if it resolves to a directory without __init__.py

Despite Python does not require __init__.py in the directory to import it,
it is better to avoid such directories for automatic source root detection.
It might cause false positives.
For example, the project might have folders like `sys`, `os` or `zlib` without any python code inside.

Space-RevId: 16539ee04d2255bc60ac0baa3d317856ca11839b

GitOrigin-RevId: 627ff4546ab4d9e5e386a6ffba6e4df38e8002a0

python/testData/quickFixes/PyMarkDirectoryAsSourceRootQuickFixTest/mysrc/foo/abc_folder_no_init.py

@@ -0,0 +1 @@
+import <error descr="No module named 'qwerty'">qwerty</error>

python/testData/quickFixes/PyMarkDirectoryAsSourceRootQuickFixTest/mysrc/foo/abc_folder_no_init_after.py

@@ -0,0 +1 @@
+import qwerty

python/testData/quickFixes/PyMarkDirectoryAsSourceRootQuickFixTest/mysrc/foo/abc_folder_with_init.py

@@ -0,0 +1 @@
+import qwerty_with_init

python/testData/quickFixes/PyMarkDirectoryAsSourceRootQuickFixTest/mysrc/foo/abc_folder_with_init_after.py

@@ -0,0 +1 @@
+import qwerty_with_init