[SM6.10] Add built-in type for LinAlg Matrix handle

[hekota]

Adds a built-in type __builtin_LinAlgMatrix that will be used in LinAlg Matrix implementation for SM 6.10.

Closes #8121

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[damyanp]

LGTM, but you probably want an approval from someone more knowledgeable.

[V-FEXrt]

About to start a deeper review but wanted to get this out there as quickly as possible.

How do you feel about __builtin_LinAlgMatrix instead of __builtin_LinAlg_Matrix?

Looking back on chat history it looks like I +1'd __builtin_LinAlg_Matrix but I must have missed the extra underscore somehow since I was surprised to see it there when I started looking at this PR.

My thoughts on why are below:

• I don't see the type as "Matrix" under the "LinAlg" feature but instead a singular noun "LinAlgMatrix" as opposed to some other noun like "CoopVecMatrix" or "GenericMatrix"
• Selfishly, I've written a lot of code using __builtin_LinAlgMatrix that would not be very fun to update

If you are okay with the change I'm more than happy to do the chore work of renaming everything

[tex3d]

Fine, but we never supported AST serialization in this code base, and there are many missing pieces already. That's why we never added the other HLSL types here.

[V-FEXrt]

LGTM*, like Damyan I'm going to leave someone else to approve since this shape of adding a type is very new looking to me :)

*of course I'd like to discuss the time name as mentioned above

[hekota]

How do you feel about __builtin_LinAlgMatrix instead of __builtin_LinAlg_Matrix?

• I don't see the type as "Matrix" under the "LinAlg" feature but instead a singular noun "LinAlgMatrix" as opposed to some other noun like "CoopVecMatrix" or "GenericMatrix"

I agree, __builtin_LinAlgMatrix is a better name.

[llvm-beanz]

As @tex3d pointed out the AST bitcode serialization is effectively untestable because it's all totally broken, but the change looks good and reasonable to me.