Add local memory parameter update functionality to sycl graphs.

Updates the sycl graph specification to add the dynamic_accessor,
dynamic_local_accessor and dynamic_work_group_memory classes.

This adds the required functionality to support updating local
memory parameters to sycl graph kernel nodes.

Additionally, it also moves the accessor update functionality
from the dynamic_parameter class to the new dynamic_accessor
class. This improves the cohesion of the API and removes
the need to use placeholder accessors when updating buffer arguments
in sycl graphs.

Author: fabiomestre