Report a better error if the order of `extends` and `implements` is swapped

```
error: 'extends' most come before 'implements'
class T implements A extends B {}
                     ^
```
PiperOrigin-RevId: 346587630
3 files changed
tree: a1e8aac5b41f6b2620698c1a390748807b8bdb5e
  1. .github/
  2. java/
  3. javatests/
  4. proto/
  5. .gitignore
  6. .travis.yml
  7. appveyor.yml
  8. LICENSE
  9. pom.xml
  10. README.md
README.md

Turbine

Turbine is a header compiler for Java.