[FEATURE] Add support for `pragma`

[TheGupta2012]

Feature Description

• Add support for pragma in openqasm

Implementation (Optional)

• Since the structure of #pragma annotations are left for the compiler to handle, we can now have key value pairs such as -

pragma __device_name__ : "simulator_1" 
pragma __device_native_gates__ : { "h", "cx", "s", "t" }

• We can have a list of predefined pragma identifiers such as __device_name__, __native_gate_set__, __device_qubits__, and so on, with a specified value schema. Following is a good place to start -

  • __device_name__ : string
  • __device_num_qubits__ : string
  • __device_native_gates__ : set of string
  • __device_architecture__ : string

• Any other pragma values are ignored or optionally stored as key value pairs without parsing the value further