Extension for the Eclipse Java IDE

**What problem does this solve?**

Brings Harper grammar checking for coders to an important IDE.

Yes Eclipse is awful to use but when working on Ghidra it's the only choice. It has tons of users, is open source, and remains in active development.

**Proposed Solution**

Pretty sure Eclipse has a wide-ranging extension API etc.

**Component**
- [ ] Core engine
- [x] Plugin/Extension
- [ ] Other: _____

Start by reviewing Harper's plugin/extension entry points and Eclipse's extension API. The issue provides no file or test to run; done would be a working Eclipse extension that brings Harper grammar checking to Eclipse users.

Written by the indexing model from the issue text.