Immutable type/struct/enum objects, allowing deduplication for reduced memory usage.

In C++ API, modifying or creating types, structures, or enumerations
should be done with the new TypeBuilder, StructureBuilder, and
EnumerationBuilder objects, then converted to a final Type, Structure,
or Enumeration object using the Finalize method once the modifications
are complete. When modifying structures or enumerations inside existing
types, use the WithReplacedStructure or WithReplacedEnumeration methods
on the root type object and reregister the type to use the modified object.

In Python API, types, structures, and enumerations can be created as in
previous versions, but the objects become immutable once they are passed
to a method. To modify an existing type, structure, or enumeration, use the
mutable_copy() method. When modifying structures or enumerations, replace
the modified object in the Type with the with_replaced_structure() or
with_replaced_enumeration() methods.