Float constant is changed to incorrect value

When I try to define a constant as
```
maxFloatAsFloat : Float
maxFloatAsFloat =
18446744073709549568.0
```
`elm-format` changes that to
```
maxFloatAsFloat : Float
maxFloatAsFloat =
18446744073709550000.0
```

This is incorrect. Value `18446744073709549568.0` can be represented **exactly** as a `Float` unlike `18446744073709550000.0`.

p.s. This is largest possible `Float` value less than `2^64`, i.e. `2^64 - 2048`.

Start by reproducing the formatting change with the Float constant shown in the issue, then trace elm-format's numeric-literal formatting path. Confirm that formatting preserves the exact value 18446744073709549568.0 rather than changing it to 18446744073709550000.0, and add or update coverage for this case if the relevant test location is found.

Written by the indexing model from the issue text.