Since the introduction of `OpAsm{Type,Attr}Interface` (#121187), it is
possible to generate alias in AsmPrinter solely from the type/attribute
itself without consulting the `OpAsmDialectInterface`. This means the
behavior can be put in tablegen file near the type/attribute definition.
A common pattern is to just use the type/attr mnemonic as the alias.
Previously, like #130479/#130481/#130483, this means adding a default
implementation to `extraClassDeclaration` in `LLVM_Attr` base class.
However, as attribute definition may override `extraClassDeclaration`,
it might be preferred to have a new field in tablegen to specify this
behavior.
This commit adds a `genMnemonicAlias` field to `AttrOrTypeDef`, when
enabled, makes `mlir-tblgen` emit a default implementation of `getAlias`
using mnemonic. When `OpAsm{Attr,Type}Interface` is not specified by the
user, `tblgen` will automatically add the interface.
For users wanting other alias behavior, they can ignore such field and
still use `extraClassDeclaration` way.
3f03f530c7