Split the `dec2flt::RawFloat` trait for easier reuse
`RawFloat` is an internal trait with quite a few useful float properties. It currently resides in the `dec2flt` module but is also used in parsing, and would be nice to reuse other places. Unfortunately it cannot be implemented on `f128` because of limitations with how the parsing API is implemented (mantissa must fit into a u64).
To make the trait easier to work with, split it into the following:
* `Float`: Anything that is reasonably applicable to all floating point types.
* `FloatExt`: Items that should be part of `Float` but don't work for all float types. This will eventually be merged back into `Float` once it can be implemented on f128.
* `Lemire`: Items that are specific to the Lemire dec2flt algorithm.
These traits are then moved to places that make sense.
Builds on top of https://github.com/rust-lang/rust/pull/151900
Jonathan Brouwer
7c6fc44b7c