[mlir] load dialect in parser for optional parameters (#96667)

https://github.com/llvm/llvm-project/pull/96242 fixed an issue where the
auto-generated parsers were not loading dialects whose namespaces are
not present in the textual IR. This required the attribute parameter to
be a tablegen def with its dialect information attached.

This fails when using parameter wrapper classes like
`OptionalParameter`. This came up because `RingAttr` uses
`OptionalParameter` for its second and third attributes.
`OptionalParameter` takes as input the C++ type as a string instead of
the tablegen def, and so it doesn't have a dialect member value to
trigger the fix from https://github.com/llvm/llvm-project/pull/96242.
The docs on this topic say the appropriate solution as overloading
`FieldParser` for a particular type.

This PR updates `FieldParser` for generic attributes to load the dialect
on demand. This requires `mlir-tblgen` to emit a `dialectName` static
field on the generated attribute class, and check for it with template
metaprogramming, since not all attribute types go through `mlir-tblgen`.

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Co-authored-by: Jeremy Kun <j2kun@users.noreply.github.com>
Co-authored-by: Oleksandr "Alex" Zinenko <ftynse@gmail.com>

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