gh-39498: Apply sort and filter of walk_packages consistently
    
Previously, the sorting and filtering is only applied in case of
FileFinder. This makes it consistently applied.

Needed to make tests in #39369
pass.

### 📝 Checklist

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- [x] The description explains in detail what this PR is about.
- [x] I have linked a relevant issue or discussion.
- [ ] I have created tests covering the changes.
- [ ] I have updated the documentation and checked the documentation
preview.

### ⌛ Dependencies

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URL: #39498
Reported by: user202729
Reviewer(s): Tobias Diez

Author: Release Manager

src/sage/misc/package_dir.py

@@ -402,9 +402,9 @@ def iter_modules(path=None, prefix=''):
                     yielded[name] = 1
                     yield ModuleInfo(i, name, ispkg)
 
-    def iter_importer_modules(importer, prefix=''):
+    def _iter_importer_modules_helper(importer, prefix=''):
         r"""
-        Yield :class:`ModuleInfo` for all modules of ``importer``.
+        Helper function for :func:`iter_importer_modules`.
         """
         from importlib.machinery import FileFinder
 
@@ -423,11 +423,6 @@ def iter_importer_modules(importer, prefix=''):
 
             for fn in filenames:
                 modname = inspect.getmodulename(fn)
-                if modname and (modname in ['__init__', 'all']
-                                or modname.startswith('all__')
-                                or modname in yielded):
-                    continue
-
                 path = os.path.join(importer.path, fn)
                 ispkg = False
 
@@ -446,6 +441,18 @@ def iter_importer_modules(importer, prefix=''):
         else:
             yield from importer.iter_modules(prefix)
 
+    def iter_importer_modules(importer, prefix=''):
+        r"""
+        Yield :class:`ModuleInfo` for all modules of ``importer``.
+        """
+        for name, ispkg in sorted(list(_iter_importer_modules_helper(importer, prefix))):
+            # we sort again for consistency of output ordering if importer is not
+            # a FileFinder (needed in doctest of :func:`sage.misc.dev_tools/load_submodules`)
+            modname = name.rsplit('.', 1)[-1]
+            if modname in ['__init__', 'all'] or modname.startswith('all__'):
+                continue
+            yield name, ispkg
+
     def seen(p, m={}):
         if p in m:
             return True