[IFRT] add c-bindings for "Held" PjRt classes (#751)

* [IFRT] add c-bindings for "Held" PjRt classes

* add `ifrt_client_assemble_array_from_single_shards`

* remove some legacy commented methods

* add `ifrt_compile`

* fix program type

* readd `ifrt_pjrt_compile` and make `ifrt_compile` use default compile options

* fix `ifrt_compile`

* get `Device` from `Client`

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Co-authored-by: Avik Pal <avikpal@mit.edu>

Author: mofeing