core: usually our enum's _INVALID and _MAX special values are named after the full...

core: usually our enum's _INVALID and _MAX special values are named after the full type

In most cases we followed the rule that the special _INVALID and _MAX
values we use in our enums use the full type name as prefix (in contrast
to regular values that we often make shorter), do so for
ExecDirectoryType as well.

No functional changes, just a little bit of renaming to make this code
more like the rest.