Steps to repro:

1. Open attached project and 'SampleScene' scene;
2. In the Hierarchy select 'Area Light' gameobject;
3. Observe the Inspector panel.

Expected result:
Area light's 'Width' and 'Height' parameters are shown (see attached expected.png screenshot).

Actual result:
Area light's Width and Height parameters are not shown (see attached actual.png screenshot).
Regression introduced in 2018.3.0a2.

Notes:
- Reproducible in 2018.3.0a2;
- Not reproducible in 2018.3.0a1, 2018.2.0b9, 2018.1.5f1;
- Reproducible on Windows and OSX.