gh-118527: Intern filename, name, and qualname in code objects. (#118558)

gh-118527: Intern filename, name, and qualname in code objects. (#118558)

This interns the strings for `co_filename`, `co_name`, and `co_qualname`
on codeobjects in the free-threaded build. This partially addresses a
reference counting bottleneck when creating closures concurrently. The
closures take the name and qualified name from the code object.