Add scripts to convert specs to unicode and insert number set shim

[ahelwer]

Changes:

1. Modify CI dependency download scripts to get TLAUC
2. Add python script to convert all modules to unicode, and back
3. Add script to insert shim definitions like LOCAL ℕ ≜ Nat as necessary

None of these scripts are called in the CI at this time but they are available to be called by other repos consuming this repo.

Will help with testing for tlaplus/tlaplus#896

Also renamed RealTime.tla in Specifying Systems because the standard module was being picked up instead of it.