[clang] [HLSL] Split out the ROV attribute from the resource attribute, make it a new spellable attribute. (PR #102414)

[Damyan Pepper via cfe-commits]

================
@@ -116,12 +116,15 @@ struct BuiltinTypeDeclBuilder {
             QualType(TTD->getTypeForDecl(), 0));
     }
     // add handle member
-    llvm::SmallVector<Attr *, 2> Attrs;
     Attr *ResourceClassAttr =
         HLSLResourceClassAttr::CreateImplicit(Record->getASTContext(), RC);
     Attr *ResourceAttr =
-        HLSLResourceAttr::CreateImplicit(Record->getASTContext(), RK, IsROV);
+        HLSLResourceAttr::CreateImplicit(Record->getASTContext(), RK);
     addMemberVariable("h", Ty, {ResourceClassAttr, ResourceAttr}, Access);
+    if (IsROV)
----------------
damyanp wrote:

It would be nice if we could find a way to be more consistent with how the other attributes are added to the field, and so only follow a single pattern for adding them.

What if we arranged it so we could write:

```c++
Attr *ResourceClassAttr =
    HLSLResourceClassAttr::CreateImplicit(Record->getASTContext(), RC);
Attr *ResourceAttr =
    HLSLResourceAttr::CreateImplicit(Record->getASTContext(), RK);
Attr *ROVAttr = IsRov ? HLSLROVAttr::CreateImplicit(Record->getASTContents()) : nullptr;
addMemberVariable("h", Ty, {ResourceClassAttr, ResourceAttr, ROVAttr}, Access);
```

There may be other ways to slice it - my main request here is that we end up with a consistent way of doing this.

Remember `addMemberVariable` _only_ exists in order for us to create this `h` member, so we can adapt it to work well for this purpose.

https://github.com/llvm/llvm-project/pull/102414