The local basis is passed into the local operator kernels as a const
reference.  That means, its lvalue is not a constant expression.  Would we
pass it by value, then it's lvalue would be a constant expression (through
it's rvalue still would not).

Calling a static function of a class throuh an object with the syntax
```c++
  lb.size()
```
will evaluate the lvalue of the object.  Since that lvalue is not constant
when the object was passed by reference, the call cannot be a constant
expression.

Clang (rightly) complained about this, so write the call as
```c++
LocalBases::size()
```
where a constant expression is required.