Fix VTS failures on tests with optional inputs

RequestArgument for optional inputs should have its .hasNoValue set
and other fields left empty. The test harness was incorrectly ignoring
the hasNoValue field and initializing the offset field even for missing
arguments. That inconsistency was caught by the sample driver and caused
an invalid argument error. With this CL the test harness now populates
requests correctly for tests with intentionally missing inputs, and that
fixes lstm* and lsh_projection.

Test: VtsHalNeuralnetworksV1_0TargetTest on Angler
Bug: 63905942
Change-Id: I8729124b720f0d4163f4b9efd452f82b825b0885