[webgpu] Add fusedConv2d kernel

[axinging]

FEATURE
Fix: #2362

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This change is 

[annxingyuan]

@axinging Thank you! Our build is failing because you are trying to import fused_util from within backend_webgpu, but it only exists within core.

Could you instead import Activation from backend_util?

Also, please export FusedConv2DConfig from backend_util (currently it only exports Activation). Then in backend_webgpu you can import FusedConv2DConfig from @tensorflow/tfjs-core/dist/fused_util, adding a TODO to import it from backend_util upon the next release of core.

[annxingyuan]

Please see comment.

[annxingyuan]

Hi @axinging - is this ready for another look? Would you mind merging master into your branch and resolving any conflicts? Thank you!

[axinging]

Done，@annxingyuan

[annxingyuan]

@axinging thanks! could you do one more thing: in backend_util.ts, export {Activation, FusedConv2DConfig, FusedBatchMatMulConfig}. then they will be available with the next release of core.

[axinging]

@axinging thanks! could you do one more thing: in backend_util.ts, export {Activation, FusedConv2DConfig, FusedBatchMatMulConfig}. then they will be available with the next release of core.

Thanks @annxingyuan, it is ready now. Sorry I forget to update the backend_util in my last commit.

[annxingyuan]

Thank you @axinging !