Based on an observation that strings and arguments are always interleaved, thanks to #15832. Additionally optimize invocations where formatting parameters are unspecified for all arguments, e.g. `"{} {:?} {:x}"`, by emptying the `__STATIC_FMTARGS` array. Next, `Arguments::new` replaces an empty slice with `None` so that passing empty `__STATIC_FMTARGS` generates slightly less machine code when `Arguments::new` is inlined. Furthermore, formatting itself treats these cases separately without making redundant copies of formatting parameters.
All in all, this adds a single mov instruction per `write!` in most cases. That's why code size has increased.
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