Rename

[bentsherman]

Adds a "rename" provider, which renames a symbol (e.g. process/workflow/function, variable) and all of its references.

The only remaining question is how to deal with aliases. But I think I know what to do:

• when renaming an aliased reference, only rename the references for that alias
• when renaming an unaliased reference, only rename the unaliased references

[bentsherman]

Merged manually via eb8489d6001be8dae1d51347668850c9346ade05