Prefer instanceof Name rather than calling isName() with one argument

Unless you actually need to check that something is both a `Name` and also of the *correct* type, using `instanceof Name` directly should be a tiny bit more efficient since it avoids one function call and an unnecessary `undefined` check.

This patch uses ESLint to enforce this, since we obviously still want to keep the `isName` helper function for where it makes sense.

.eslintrc

@@ -187,6 +187,10 @@
         "selector": "CallExpression[callee.name='isDict'][arguments.length<2]",
         "message": "Use `instanceof Dict` rather than `isDict()` with one argument.",
       },
+      {
+        "selector": "CallExpression[callee.name='isName'][arguments.length<2]",
+        "message": "Use `instanceof Name` rather than `isName()` with one argument.",
+      },
       {
         "selector": "NewExpression[callee.name='Cmd']",
         "message": "Use `Cmd.get()` rather than `new Cmd()`.",