Update on "[llm] Support different shape of input_pos"

For huggingface models, `forward()` is taking `tokens` as well as `cache_positions`, which is a list of cache indices. This is different than the .pte files `export_llama` gives, which are taking `tokens` and `input_pos` where `input_pos` is a scalar tensor.

This PR adds support inside `text_decoder_runner.cpp` to handle both shapes of `input_pos`/`cache_positions`.

To make the logic more generic without relying on extra metadata, here I'm adding the logic of inspecting method meta and input tensor info, to make a decision if we want to feed in `input_pos` or `cache_position`.

Differential Revision: [D77203700](https://our.internmc.facebook.com/intern/diff/D77203700/)

[ghstack-poisoned]

Author: larryliu0820

kernels/portable/cpu/util/arange_util.cpp

@@ -38,11 +38,13 @@ void arange_out_impl(
     double end,
     double step,
     Tensor& out) {
+  (void)ctx;
   Tensor::SizesType numel = compute_arange_out_size(start, end, step);
   ET_ARANGE_IMPL(ctx, start, numel, step, out, "arange.start_out");
 }
 
 void arange_out_impl(KernelRuntimeContext& ctx, double end, Tensor& out) {
+  (void)ctx;
   ET_ARANGE_IMPL(ctx, 0.0, end, 1.0, out, "arange.out");
 }