PR: convert leoAtFile.py to leoAtFile.ts

[edreamleo]

Leo issue #2275 what Leo's python-to-typescript command does, and what it doesn't (can't) do.

Status of leoAtFile.ts

• leoAtFile.ts is exactly the output of Leo's python-to-typescript command.
• vs-code colorizes all lines correctly.
• tsc issues hundreds of errors about translated f-strings. For example:

  src/core/leoAtFile.ts:4267:45 - error TS1434: Unexpected keyword or identifier.
  4267             g.trace(`Invalid external file: ${sfn}`);

  I have no idea why tsc issues these error messages!

Summary

Imo, leoAtFile.ts is a good starting point for the final version of leoAtFile.ts, to be completed by you, Félix.

Work on Leo's python-to-typescript command is complete, for now. I'll be happy to fix bugs in this command. If you like, we can zoom to discuss any possible improvements in python-to-typescript.

[edreamleo]

Let's close this PR. It's way out of date.