PY-25234 More efficient way to check that a user skeleton belongs to the stdlib

Also, I added a test on that scenario using the skeleton for "alembic"
as an example.

python/testData/quickFixes/PyAddImportQuickFixTest/binarySkeletonStdlibModule/main.py

@@ -0,0 +1,5 @@
+import re
+
+import mod
+
+print(re, <error descr="Unresolved reference 'sys'">s<caret>ys</error>, mod)

python/testData/quickFixes/PyAddImportQuickFixTest/binarySkeletonStdlibModule/main_after.py

@@ -0,0 +1,6 @@
+import re
+import sys
+
+import mod
+
+print(re, sys, mod)