In 1e91f3b we disabled annotation processors globally. However, some
project like JMH need annotation processing, so we add an ability to
selectively enabled annotation processing for certain projects by
setting an external property in the corresponding Gradle build script.
Note that `javac` would allow to set a specific annotation processor
with the command line option `-processor`. However, due to a bug in
Gradle we we cannot use this option and need to enable all annotation
processors.
With this commit we add a benchmarks project that contains the necessary build
infrastructure and an example benchmark. It is added as a separate project to avoid
interfering with the regular build too much (especially sanity checks) and to keep
the microbenchmarks isolated.
Microbenchmarks are generated with `gradle :benchmarks:jmhJar` and can be run with
` gradle :benchmarks:jmh`.
We intentionally do not use the
[jmh-gradle-plugin](https://github.com/melix/jmh-gradle-plugin) as it causes all
sorts of problems (dependencies are not properly excluded, not all JMH parameters
can be set) and it adds another abstraction layer that is not needed.
Closes#18242