[dogfooding][cleanup] Use new StringBuffer -> StringBuilder
cleanup for tests.model

To ensure that the new JDT cleanup works correctly for clients we should
run it also on our own code base. This help to ensure that the cleanup
works fine and helps us to cleanup our own code base.

From the commit message of the cleanup:

- create a cleanup to replace usage of StringBuffer with
  StringBuilder.  The two are equivalent, but StringBuffer is
  thread-safe and synchronized which makes it slower than
  StringBuilder which was introduced in Java 1.5.

To avoid API changes, we should only use the local variable change.

Change-Id: Id573afe34c76a5861125e8af91581add14307f98
Signed-off-by: Lars Vogel <Lars.Vogel@vogella.com>
Reviewed-on: https://git.eclipse.org/r/c/platform/eclipse.platform/+/182676
Tested-by: Platform Bot <platform-bot@eclipse.org>
4 files changed