fix: Introduce fluent pattern for StopWatch

[larshelge]

This PR introduces fluent pattern for StopWatch. The goal is to improve readability and maintainability of code using StopWatch by creating a sentence-like flow of operations.

When using StopWatch the calling code gets a little verbose with operations on short, separate lines:

StopWatch watch = StopWatch.createStarted();
// Do work
watch.split();
log.info(watch.toString());
// Do work
watch.stop();
log.info(watch.toString());

A more fluent, readable and compact format could be:

StopWatch watch = StopWatch.createStarted();
// Do work
log.info(watch.split().toString());
// Do work
log.info(watch.stop().toString());

[garydgregory]

-1: This PR breaks binary compatibility. If you really want this, you can create a Jira as a feature request for a future 4.0.

[larshelge]

Noted, that is okay @garydgregory .

[garydgregory]

Closing. Maybe for 4.0, which would be in a different package.