TosaToTensor: Support reshape on tensors of unsigned integer (#91734)

This adds 
- `mlir::tosa::populateTosaToLinalgTypeConversion` which converts
tensors of unsigned integers into tensors of signless integers
- modifies the `tosa.reshape` lowering in TosaToTensor to use the type
converter correctly

I choose to implement the type converter in
`mlir/Conversion/TosaToLinalg/TosaToLinalg.h` instead of
`mlir/Conversion/TosaToTensor/TosaToTensor.h` because I need the same
type converter in the TosaToLinalg lowerings (future PR).
Alternatively, I could duplicate the type converter so it exists both in
TosaToLinalg and TosaToTensor. Let me know if you prefer that.