Shader Build Settings keyword overrides not matching with different empty keyword forms

The shader build settings requires exact match of the keyword list to apply given keyword declaration overrides. However, the users would expect "empty keyword" to be the same no matter how many underscores is used to spell it out (as this is how it works otherwise). Requiring the exact match in the empty keyword case can be really confusing for users trying to use the shader build settings.

 

Steps to reproduce:

1. Create a shader with multi_compile using multiple underscores as the "empty keyword"
2. Create a keyword declaration override in the shader build settings targeting that multi_compile but using single underscore as the "empty keyword"

Actual results: 

The keyword declaration override does not take effect on the shader.

Expected results: 

The keyword declaration override affects the shader.

Reproducible with versions: 

Not reproducible with versions: 

Can’t test with versions: 

Tested on (OS): 

Notes:

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