Add AmbientAndDiffuse cases for determining light and material
parameter count.

Define default cases as UNREACHABLE for GetLightModelParameterCount,
GetLightParameterCount and GetMaterialParameterCount.

Bug: angleproject:5751
Change-Id: I58acb62e66cea71277654313800dafa57c42b17e
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2871794Reviewed-by: Cody Northrop <cnorthrop@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Lubosz Sarnecki <lubosz.sarnecki@collabora.com>