This PR is quite similiar to #174700.
In this PR, I added a C API for each (upstream) MLIR attributes to
retrieve its name (for example, `StringAttr -> mlirStringAttrGetName()
-> "builtin.string"`), and exposed a corresponding type_name class
attribute in the Python bindings (e.g., `StringAttr.attr_name ->
"builtin.string"`). This can be used in various places to avoid
hard-coded strings, such as eliminating the manual string in
`irdl.base("#builtin.string")`.
Note that parts of this PR (mainly mechanical changes) were produced via
GitHub Copilot and GPT-5.2. I have manually reviewed the changes and
verified them with tests to ensure correctness.
This add the basic APIs to create VariadicityAttr and
VariadicityArrayAttr attributes from the C API. This is necessary for
C API users that want to create IRDL dialect declarations.
Being able to add custom dialects is one of the big missing pieces of
the C API. This change should make it achievable via IRDL. Hopefully
this should open custom dialect definition to non-C++ users of MLIR.
