Auto merge of #97480 - conradludgate:faster-format-literals, r=joshtriplett

Auto merge of #97480 - conradludgate:faster-format-literals, r=joshtriplett

improve format impl for literals

The basic idea of this change can be seen here https://godbolt.org/z/MT37cWoe1.

Updates the format impl to have a fast path for string literals and the default path for regular format args.

This change will allow `format!("string literal")` to be used interchangably with `"string literal".to_owned()`.

This would be relevant in the case of `f!"string literal"` being legal (https://github.com/rust-lang/rfcs/pull/3267) in which case it would be the easiest way to create owned strings from literals, while also being just as efficient as any other impl