Add symlinks sanity test. (#46467)

* Add symlinks sanity test.
* Replace legacy test symlinks with actual content.
* Remove dir symlink from template_jinja2_latest.
* Update import test to use generated library dir.
* Fix copy test symlink setup.

test/sanity/code-smell/symlinks.json

@@ -0,0 +1,4 @@
+{
+    "always": true,
+    "output": "path-message"
+}

test/sanity/code-smell/symlinks.py

@@ -0,0 +1,35 @@
+#!/usr/bin/env python
+
+import os
+
+
+def main():
+    skip_dirs = set([
+        '.tox',
+    ])
+
+    for root, dirs, files in os.walk('.'):
+        for skip_dir in skip_dirs:
+            if skip_dir in dirs:
+                dirs.remove(skip_dir)
+
+        if root == '.':
+            root = ''
+        elif root.startswith('./'):
+            root = root[2:]
+
+        for file in files:
+            path = os.path.join(root, file)
+
+            if not os.path.exists(path):
+                print('%s: broken symlinks are not allowed' % path)
+
+        for directory in dirs:
+            path = os.path.join(root, directory)
+
+            if os.path.islink(path):
+                print('%s: symlinks to directories are not allowed' % path)
+
+
+if __name__ == '__main__':
+    main()