Directional lights shadows displays visual artefacts when viewed at an angle/at a distance in the Scene view.

Repro steps:
1. Open TestScene from attached project.
2. In the scene view, tilt the view back and forward and zoom in and out.
3. Observe visual artefacts appearing on the plane.

Expected outcome: no visual artefacts.

Notes:
- Issue appears in both gamma and linear color space, and in all lighting paths except for Legacy Vertex Lit.
- Issue does not seem to be API specific.
- Issue does not appear with other light types: only with directional
- Increasing shadow bias somewhat alleviates the issue.
- Regression: appears first in 5.4.0b5 (not reproduceable in 5.4.0b4)