strconv: use DragonBox instead of Ryu for FormatFloat

[snadrus]

DragonBox is a faster algorithm.
NodeJS has already switched as part of accelerating JSON.stringify().
Float to string conversion is used by effectively all Go software, so even a small speed up could be helpful.

This change effects the standard library implementation only. No API changes or functionality changes are part of this proposal.

[seankhliao]

not a proposal since there's no API change.
feel free to submit a CL with benchmark results.

[thepudds]

Some references:

https://github.com/jk-jeon/dragonbox?tab=readme-ov-file#to-people-wanting-to-port-the-algorithm

Those who want to port the algorithm into other languages or re-implement it from scratch are recommended to look at the simpler implementation first rather than the main implementation, since the main implementation is riddled with template indirections obscuring the core logic of the algorithm.