Improve entry point lookup function documentation

[aleino-nv]

• Add a unit test for the case where the code does not specify entry points, but they are instead specified via the API
• Make the entry point lookup logic check the information in the options
• Add user guide documentation that explains which lookup function to use when there is no [shader(...)] attribute on an entry point
• Add a documentation comment in slang.h mentioning the restriction on findEntryPointByName

#6452

See also issue #4760.

[cheneym2]

Looks good to me, but someone else should approve

[csyonghe]

There is no bug to be fixed here. If the source code did not specify [shader()] attribute, the host side should call findAndCheckEntryPoint.

[aleino-nv]

There is no bug to be fixed here. If the source code did not specify [shader()] attribute, the host side should call findAndCheckEntryPoint.

@csyonghe IIUC the user guide just states that [shader(...)] should not be needed: #4760 (comment). I don't find any mentions of findAndCheckEntryPoint.
It seems pretty obscure to me that leaving off [shader(...)] would mean you need to call one particular API rather than another similar one.

I ran into this because several tests don't specify [shader(...)], and those fail to look up entry points when I migrate away from the deprecated build request API.

[csyonghe]

It is documented here: https://shader-slang.org/docs/compilation-api/#query-entry-points

[aleino-nv]

At least I see this doc comment for findAndCheckEntryPoint:

    /// Find and validate an entry point by name, even if the function is
    /// not marked with the `[shader("...")]` attribute.
    virtual SLANG_NO_THROW SlangResult SLANG_MCALL findAndCheckEntryPoint(...)

The findEntryPointByName function should probably also have a doc comment that mentions this, and the user guide should probably direct the user to findAndCheckEntryPoint.

I will change the patch accordingly.

[aleino-nv]

@csyonghe I added a mention in the user guide and slang.h as well. I think it's worth mentioning there since it would have saved me some time...

[csyonghe]

looks good! needs a formatting fix.

[aleino-nv]

/format

[slangbot]

🌈 Formatted, please merge the changes from this PR