Implement str and bool runtime functions

[namannimmo10]

Inspiration: #1 (comment)

[namannimmo10]

We should do something about this line:

lpython/src/libasr/codegen/asr_to_llvm.cpp

Line 1518 in e1b2778

throwCodeGenError("Unsupported len value in ASR");

Nonetheless, the ASR looks good to me.

[certik]

Is this an intrinsic function? I don't see it here: https://docs.python.org/3/library/functions.html

Also it's time to refactor this whole function into LFortran's style. Let's not put anymore functions here until we refactor, as it is unmaintainable longterm. Let me know if you know how to do the refactor.

[namannimmo10]

Is this an intrinsic function?

No. We will add a generic function, str() down the road, but right now I'm trying to make str_int and str_float work.

I have two ideas for doing that:

1. Using decorators...
2. Using type guard:

>>>defstr(val: i32|f64):
... # "isinstance" type guard
... ifisinstance(val, i32):
... # type of `val` is narrowed to `i32`
... returnstr_int(val)
... elifisinstance(val, f64):
... # else, type of `val` is narrowed to `f64`
... returnstr_float(val)
...
>>>

You are talking about this file, right?

[namannimmo10]

Once we merge this, I will add the rest.

[certik]

I think that this looks great!