[Fogbugz 1324000] Fixing unlit emissive reflections

[kecho]

Purpose of this PR

Fixing fogbugs: https://fogbugz.unity3d.com/f/cases/1324000/
Unlit emissive was too dark, because there was a missing pre exposure multiplication.

Repro steps :

• Open attached project
• Open SampleScene_Exposure0
• Notice that both lit and unlit ray traced reflection looked similar
• Now open SampleScene_Exposure_12
• It's the same scene with fixed exposure of 12, HDRI sky exposed to 12 and higher intensity dir light

Expected : Same result as the non exposed scene
Result : Unlit emissive is black.

Before:

After:

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Testing status

• Tested with many levels of exposure in the unlit material, and now the material behaves correctly.
• Tested on PC with auto exposure and several fixed exposure values.
• Running all platforms tests (DXR and standard). Likely we might need screenshot update.

[sebastienlagarde]

@remi-chapelain can you ensure this is cover in one of our test. Also guess we need to check for both unlit with emissive and lit with emissive.

[sebastienlagarde]

@kecho in your test, is your mesh emissive only or does it have a color + emissive contribution? (we should check the later if not check)

[kecho]

@kecho in your test, is your mesh emissive only or does it have a color + emissive contribution? (we should check the later if not check)

My test is emissive only, black color. I did test with color as well and looked correct.

[remi-chapelain]

I'll add a test in DXR Test project in this PR as stated in the bug and take care of screenshots if some needs updating.

[remi-chapelain]

Verified the fix quickly.

Added 4 tests to cover reflections of emissive

• Low exposure perf mode
• high exposure perf mode
• Low exposure quality mode
• high exposure quality mode

High and low exposure look the same because the value of emissive and sun are adjusted accordingly. Only noticeable difference is the reflection resolution in performance vs quality;

Ran all DXR Tests locally (All 🟢, which proved we didn't have proper coverage for this) since yamato is overloaded, I'd say we're good to merge without testing remotely