Service files should be merged by default

### What feature do you want to see added? Shadow can easily merge service files using `mergeServiceFiles()` - this matches the behavior of non-shaded dependencies. However, this is not enabled by default, meaning that by default the behavior of service loaders differs between shaded and un-shaded jars. I think that it should not, and the merging of service files should be the default state. ### Upstream changes _No response_ ### Are you interested in contributing this feature? Sure, if it's as easy as calling `mergeServiceFiles()` when setting up the task.