[Stream] Update dispatch sites encodings in UnifyEncodingForGlobals pass 2/n

[hanhanW]

Added functionality to update stream.tensor.dispatch operand encodings when unifying encodings for globals.

• Uses Explorer with walkTransitiveUses for cross-function tracking of encoded global uses.
• Follows stream.async.clone ops (BFS worklist) to collect updates. Currently, only stream.tensor.dispatch op is updated. Other ops that have TensorPhaseOp are not implemented yet.
• Applies all updates in one shot using DenseMap<Operation*, DenseMap<unsigned, Attribute>>. This makes update more efficient because we don't have to iterate all the encoding operands in every update.

New tests:

• Basic dispatch with encoded operand.
• Multiple encoded operands in same dispatch (@use_both_encodings).
• Cross-function tracking via util.call (@cross_function_call → @dispatch_helper).

It is a step towards https://github.com/iree-org/iree/issues/22485

[hanhanW]

I found few issues when I added few more tests. I'll open it after I fix it.