Disable implicit casting by default and implement intrinsic functions for casting - #1194

Thanks for working on this! This was on my TODO list, I think we want to do this change soon, since it's a breaking change.

We don't need to add the compiler flag in this PR. If there is a need, we can add it later.

@certik, The functions are mainly working fine. I have to work on the BinOp casting (for example - making i32(3.2 + 1.5) work) and a few other things before I can complete this PR. However, there are a few things where I need some help -

$ cat examples/expr2.py
from ltypes import i32

def main0():
    x: f64
    x = i32(6.8)
    print(x)

main0()
$ lpython examples/expr2.py
semantic error: Type mismatch in assignment, the types must be compatible
 --> examples/expr2.py:5:5
  |
5 |     x = i32(6.8)
  |     ^       ^^^ type mismatch ('f64' and 'i32')


Note: if any of the above error or warning messages are not clear or are lacking
context please report it to us (we consider that a bug that needs to be fixed).

Here the error message should point to the complete i32() part but it instead, it just points to the argument passed. Ideally, it should be -

  |
5 |     x = i32(6.8)
  |     ^   ^^^^^^^^ type mismatch ('f64' and 'i32')

How can I fix this?

You have to pass in the location information of the i32 node, not the argument 6.8.

Any progress on this? I think we need to this early especially for the following cases,

1. Casting while passing function arguments.
2. Casting while passing initial values to constructors.

@akshanshbhatt If you don't have time then let me know I can finish this as I anyways need this to happen. Thanks.

Self-assigning. I will complete this tomorrow. Thanks.

Closing in favour of #1271

Closing in favour of #1271

Thanks for working on this, @czgdp1807! I just saw your previous messages on this PR; sorry for that - I was busy with my midsemester exams.