[BUG] String.__repr__() does not handle escape quotes or complexe situations

[gabrieldemarmiesse]

Bug description

The current implementation of String.__repr__() is very simple and is enough for simple use cases. If the String has simple quotes and double quotes in it, then things start to break. We should also be able to handle \ and such. As a reminder the output of String.__repr__() should produce a String which can be copy-pasted into a mojo file to recreate the same string. (like in python)

From what I understand the implementation in CPython is here: https://github.com/python/cpython/blob/main/Objects/unicodeobject.c#L12256 and while it's complicated, this is because it handles Unicode, which we don't have yet in Mojo. If we only support ASCII, that should be enough for now.

Steps to reproduce

print(repr(String("''\'\\")))

should return a valid Mojo expression but returns "'''\' instead which is not a valid Mojo expression.

System information

Ubuntu 22.04
mojo 2024.4.2923 (f54d89e3)
modular 0.7.2 (d0adc668)

[helehex]

I was just gonna copy over my naïve lookup table, but maybe i should do it a little better

[helehex]

seems like theres some move towards unicode anyways

[helehex]

here's a solution
#2493