RFR: 8263038: Optimize String.format for simple specifiers [v2]

[Claes Redestad]

On Fri, 5 Mar 2021 16:36:19 GMT, Roger Riggs <rriggs at openjdk.org> wrote:

>> Claes Redestad has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Lazily evaluate zero
>
> Looks good.

Piling on another optimization: The `getZero(..)` called eagerly in the constructor is rather expensive in non-US locales, e.g. running with "-Duser.language=fr":
Benchmark                  Mode  Cnt    Score     Error  Units
StringFormat.stringFormat  avgt    5  924.536 ± 253.151  ns/op
Since the zero value is only used when printing floating point number I refactored so that the localized zero is evaluated lazily, which gets numbers on the micros in line with the numbers for a US locale:
Benchmark                  Mode  Cnt    Score    Error  Units
StringFormat.stringFormat  avgt    5  291.385 ± 64.626  ns/op

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PR: https://git.openjdk.java.net/jdk/pull/2830