In this PR, I added a C API for each (upstream) MLIR type to retrieve
its type name (for example, `IntegerType` -> `mlirIntegerTypeGetName()`
-> `"builtin.integer"`), and exposed a corresponding `type_name` class
attribute in the Python bindings (e.g., `IntegerType.type_name` ->
`"builtin.integer"`). This can be used in various places to avoid
hard-coded strings, such as eliminating the manual string in
`irdl.base("!builtin.integer")`.
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.
