Integrate StableHLO at openxla/stablehlo@65b9091d71b9
Integrate StableHLO at openxla/stablehlo@65b9091d71b9

Manually updated files:
  * lib/Dialect/mhlo/transforms/hlo_legalize_to_stablehlo.cc
  * tests/Dialect/mhlo/hlo-legalize-to-stablehlo.mlir
  * tests/Dialect/mhlo/stablehlo-legalize-to-hlo.mlir

Manual updates were needed to accommodate StableHLO dropping support for "unknown" dimensions in ConvDimensionNumbers. See https://github.com/openxla/stablehlo/pull/360 as well as this commit for details.

PiperOrigin-RevId: 485784217

google/tsl,google/tsl,google/tsl