Grammar Check with Harper

**Is your feature request related to a problem?**
Lightweight and quick grammar checker.

**Describe the solution you'd like**
Using Harper: https://github.com/Automattic/harper

**Use case**
It checks grammar rather quickly even though it's less accurate than say LanguageTool or AI proofread. Even then, it is lighter.

**Alternatives considered**
LanguageTool

**App version & Flavor**
--
