This patch expose the type and attribute names in C++ as methods in the
`AbstractType` and `AbstractAttribute` classes, and keep a map of names
to `AbstractType` and `AbstractAttribute` in the `MLIRContext`. Type and
attribute names should be unique.
It adds support in ODS to generate the `getName` methods in
`AbstractType` and `AbstractAttribute`, through the use of two new
variables, `typeName` and `attrName`. It also adds names to C++-defined
type and attributes.