to_float and infinity result can crash vector

[dhable]

We ran into an issue where parsing a string with to_float exceeds the bounds of f64::MAX, which returns a non-error infinity value.

$ str_value = "61687855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562"
"61687855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562"

$ parsed_value, err = to_float(str_value)
inf

$ err
null

Since err was null, it's might seem like it's safe to perform operations on this value but subtraction causes vector to panic and crash. This is because f64::INFINITY - f64::INFINITY == f64::NAN in rust.

$ parsed_value + parsed_value
inf

$ parsed_value + 1
inf

$ parsed_value - 1
inf

$ 1 - parsed_value
-inf

$ parsed_value - parsed_value
thread 'main' panicked at /Users/dan.hable/.cargo/registry/src/index.crates.io-6f17d22bba15001f/ordered-float-4.2.2/src/lib.rs:1331:37:
Subtraction resulted in NaN: FloatIsNan
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

I can't find anything in the VRL language, besides using to_string to compare with "inf", that would allow me to detect this situation and avoid operations on infinite values. IMHO, I would have expected an error result instead of infinity, similar to how to_int behaves.

$ parsed_value, err = to_int(str_value)
"function call error for \"to_int\" at (20:29): Invalid integer \"61687855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562855628556285562\": number too large to fit in target type"

[pront]

Thanks @dhable, I will take a look. Need to think a bit about the breaking behavior of this change.

[pront]

I think the proposed (breaking) change makes sense. See playground examples. We can make the check even stricter by using is_normal.