[C++][Python] Remove integer compatibility for trunc, floor and ceil

[js8544]

Describe the enhancement requested

Follow-up of #36289 (comment). I am in favor of removing integer compatibility for trunc, floor and ceil for the following reasons:

1. Mathematically they are no-ops for integers, so it doesn't make much sense to support them as a function.
2. The current implementation casts ints to floats, which may yield unexpected results due to float precision issues.
3. It's very simple to remove it, by just deleting several lines of code, as @jorisvandenbossche mentioned here, along with some small changes in tests and docs.
4. The support for integers was probably unintentional, just like the case for round.

The downside is, all the SQL engines, along with Numpy and R, support floor(int), and the result type is double, which means our current implementation is consistent with them.

cc @pitrou @jorisvandenbossche @westonpace

Component(s)

C++

[pitrou]

I'm fine with either removing or keeping integer input support.

@jorisvandenbossche What do you think?

[js8544]

cc @jorisvandenbossche would you mind taking a look?