[RELAY] Re-wrote the Graph Partitioner to support multiple outputs (a…

…pache#5143)

* [RELAY] Re-wrote the Graph Partitioner to support multiple outputs

Input : A Relay module that have functions with disjoint annotated regions
        using compiler_begin and compiler_end. There could be multiple outputs.

Output : A Relay module with global functions for such disjoint annotated regions
         with calls inserted at the respective location

Dependencies : AnnotatedRegionSet Utility class.

Methodology :
      1) The AnnotatedRegionSet utility class is able to construct a collection of
         nodes that are bound by a give annotation -- here we use compiler_begin
         and compiler_end
      2) Initially, for each function in the module AnnotatedRegionSets are populated.
      3) Then, Vistor pass is traversed until a compiler_end node is encountered
         that belongs to a "region".
      4) When the first compiler_end of a given annotated region is found, a function is
         formed and inserted.
         a) if the region has multiple outputs, a Tuple node (capturing all outputs)
            is returned.
      5) Thereafter, if we encounter an another output of the same annotated region,
         it is important to note that the function is already formed. Therefore, it will
         lookup the function and add a TupleGetItemNode is inserted.
          a) We will use the location index of "rets" of each "Region" of AnnotatedRegionSet
             as TupleGetItemNode index.
      6) Therefore, functions will be created for all annotated regions. The name for each
         global function is created using "Region" id and the compiler name.

Change-Id: I1372f02a845b6d3da03b561763e03a378dca263c

* [RELAY] Re-wrote the Graph Partitioner to support multiple outputs

    *removed the expected use-case as we are taking broken-down PR approach
    *code style fixes
    *some trivial one liners

* [RELAY] Re-wrote the Graph Partitioner to support multiple outputs

    *fixed an implicit copy to a move

* [RELAY] Re-wrote the Graph Partitioner to support multiple outputs

    *code style changes for comments
    *renamed test case multiple outputs --> mixed single multiple outputs
        Since the existing test case checks for both single and multiple
        output scenarios
    *added a new test case with conv2d + batch_norm
    *some var name changes in the test

* [RELAY] Re-wrote the Graph Partitioner to support multiple outputs

	*rebased