Mark num_outputs as out parameter in PJRT_Executable_OutputDimensions_Args Fixes #25211

[grewalsk]

Fixed #25211 by updating the C API header to explicitly mark num_outputs as an output parameter, clarifying the API contract. I also added a new C API test that calls GetOutputDimensions and verifies that num_outputs, dims and dim_sizes are correctly populated.

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[grewalsk]

Im having some trouble with the CLA agreement it says an email contributed that, I will fix that and then redo it.

[allanrenucci]

Closing due to inactivity.