tint: Stub intrinsic @const evaluation

Add support for @const to builtins in intrinsics.def.
Propagate this flag through to the intrinsic table.
Handle builtins that are @const annotated in the resolver.

Currently no intrinsics are decorated with @const, so there's nothing to
test (yet).

Bug: tint:1504
Change-Id: I172483688617782bd7c58b70e3f38d0222a5d1af
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/92323
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>

tools/src/cmd/intrinsic-gen/gen/builtin_table.go

@@ -105,6 +105,8 @@ type Overload struct {
 	IsDeprecated bool
 	// The kind of overload
 	Kind string
+	// The function name used to evaluate the overload at shader-creation time
+	ConstEvalFunction string
 }
 
 // Intrinsic is used to create the C++ IntrinsicInfo structure
@@ -206,6 +208,7 @@ func (b *IntrinsicTableBuilder) buildOverload(o *sem.Overload) (Overload, error)
 		CanBeUsedInStage:           o.CanBeUsedInStage,
 		IsDeprecated:               o.IsDeprecated,
 		Kind:                       string(o.Decl.Kind),
+		ConstEvalFunction:          o.ConstEvalFunction,
 	}, nil
 }