refactor(tvix/eval): rename OpAttrsIsSet -> OpHasAttr

This matches the name of the AST node from which it was compiled.
Suggested by sterni in cl/6231

Change-Id: Ia51525158d2f47467c01fce2282005b1a8417a47
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6623
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
Reviewed-by: grfn <grfn@gws.fyi>

tvix/eval/src/compiler/attrs.rs

@@ -256,7 +256,7 @@ impl Compiler<'_, '_> {
 
         // After the last fragment, emit the actual instruction that
         // leaves a boolean on the stack.
-        self.push_op(OpCode::OpAttrsIsSet, &node);
+        self.push_op(OpCode::OpHasAttr, &node);
     }
 
     pub(super) fn compile_select(&mut self, slot: LocalIdx, node: ast::Select) {