Rename IR classes so names do not clash with others.

I noticed that the `TypeConversion` class from Slither IR

https://github.com/crytic/slither/blob/5021f3e7a04e46dd32655f8d168b43a8bb000770/slither/slithir/operations/type_conversion.py#L7

has the same name as another class from Slither Core

https://github.com/crytic/slither/blob/5021f3e7a04e46dd32655f8d168b43a8bb000770/slither/core/expressions/type_conversion.py#L6

This makes it so that, if you are not extra careful, you can import the wrong class.

I think that it would be a good idea to go through all the classes and look for those that have name clashes across different "packages" and rename them, for example by adding an `IR` suffix to them (`TypeConversionIR`).

NOTE:

This might apply to different packages i.e not only SlitherIR, in which case a different suffix would need to be added.