Support bulk defining/modifying types for data vars in a selection

Right now we already support bulk defining integer types by pressing 1, 2, 4, 8. A user recently brought up a use case which suggests we might wish to extend this functionality to:

1. bulk defining such types even if they are not integers. For example, the user might wish to define several enums over a range. Putting them in an array might be an optional in certain cases, but there are still many cases where they are not related, so putting them in an array is not a good idea

2. bulk changing the type. The user brought up a case where he has several strings with the type "char*", and he wishes to change them to "const char*". This is not easy to carry out now. It would be great if we support bulk modifying the types in a selection. I have also ran into a similar situation where I get several integers, and I wish to change all of them to const type.

Start by locating the existing bulk integer type-definition action and the selection and data-variable type APIs. Compare the requested bulk definition and bulk modification cases, including non-integer types and const-qualified pointer types. Done means both operations work across a selection without requiring the variables to be placed in an array.