Remove unused type_is_pod function
Implement `has_dtor` method in TypeContents
Keep track of Enum's with destructors
Forbid moves out of static items Closes #10577
Forbid certain types for static items

- For each *mutable* static item, check that the **type**:
    - cannot own any value whose type has a dtor
    - cannot own any values whose type is an owned pointer

- For each *immutable* static item, check that the **value**:
    - does not contain any ~ or box expressions
        (including ~[1, 2, 3] sort of things)
    - does not contain a struct literal or call to an enum
        variant / struct constructor where
        - the type of the struct/enum has a dtor
Closes #9243 Test case
Closes #7364 Test case
Immutable static items should be `Freeze` Fixes #12432