[MLIR][LLVM] Support dso_local_equivalent constants (#132131)

Create a new operation `DSOLocalEquivalentOp`, following the steps of
other constants.

This is similar in a way to `AddressOfOp` but with specific semantics:
only support functions and function aliases (no globals) and extern_weak
linkage is not allowed.

An alternative approach is to use a new `UnitAttr` in `AddressOfOp` and
check that attribute to enforce specific semantics in the verifiers. The
drawback is going against what other constants do and having to add more
attributes in the future when we introduce `no_cfi`, `blockaddress`,
etc.

While here, improve the error message for other missing constants.

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