Extra allocations in `*TextFormatWriter` because of Java 8 target

See this line of code:

https://github.com/prometheus/client_java/blob/fa68aa7789c53d54ea1783f120194a3feae7e7b8/prometheus-metrics-exposition-textformats/src/main/java/io/prometheus/metrics/expositionformats/OpenMetricsTextFormatWriter.java#L412

Because of the Java 8 target, the string concatenation gets compiled to something like new StringBuilder().append(name).append(suffix).toString(), which allocates the memory at least twice (for the buffer in the StringBuilder and for the resulting string).

If the code was compiled for at least Java 9, it would use StringConcatFactory, which in this case would allocate the memory only for the resulting string.

Would the maintainers consider publishing multiple artifacts for different Java targets, or using multi-release JARs for the purpose of this and similar optimizations?

Start with OpenMetricsTextFormatWriter.java at the linked line and review how the project targets Java 8. Then investigate the artifact-publishing and multi-release JAR options described in the issue. Done would be a documented, maintainer-approved approach for reducing these allocations across the relevant TextFormatWriter code.