Allow to opt-out of loading shaders from original location

[azeno]

PR Details

This PR adds a property to the ShaderSourceManager which allows to opt-out of the system trying to load from the original path first.
We ran into this issue several times in the past that on build machines our app would behave differently or not run at all because it would load shaders in a different state than the app was build with.

Types of changes

• Docs change / refactoring / dependency upgrade
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My change requires a change to the documentation.
• I have added tests to cover my changes.
• All new and existing tests passed.
• I have built and run the editor to try this change out.

[xen2]

From top of my head, it was for either (or both) of those scenarios (dev/desktop only):

• map to real source file (#file and #line info for debugger), otherwise any shader debugger can't trace into original source if there is no actual file
• hot reload

Sounds good to me to have a flag for now, I will eventually get back to it with new shader system anyway.