Resolve conflicts in nodeAgg.h and nodeAgg.c

[RekGRpth]

1. Commit 9878b64 in src/include/executor/nodeAgg.h changed the
   input_groups argument's type from uint64 to double in the definition of
   the hash_agg_set_limits function. However, the earlier commit 19cd1cf
   had already added a new first argument, AggState *aggstate.

2. Commit 9bdb300 in src/include/executor/nodeAgg.h added definitions
   of the new functions ExecAggEstimate, ExecAggInitializeDSM,
   ExecAggInitializeWorker, and ExecAggRetrieveInstrumentation. Earlier
   commits 6195b96 and a759b72 had already added definitions of the
   functions ExecSquelchAgg and ReuseHashTable in the same location.

3. Commit 9878b64 in src/backend/executor/nodeAgg.c changed the
   input_groups argument's type from uint64 to double in the functions
   hash_choose_num_partitions, hashagg_spill_init, and
   hash_agg_set_limits. However, the earlier commit 19cd1cf had already
   added a new first argument, AggState *aggstate.

4. Commit d6c08e2 in src/backend/executor/nodeAgg.c changed the
   work_mem variable to hash_mem in the functions hash_agg_set_limits and
   hash_choose_num_partitions. However, earlier GPDB-specific commits had
   already replaced it with strict_memlimit.

5. Commit 9878b64 in src/backend/executor/nodeAgg.c changed the
   ngroups_estimate argument to batch->input_card in the
   agg_refill_hash_table and agg_refill_hash_table functions when calling
   hash_agg_set_limits and hashagg_spill_init. However, the earlier commit
   19cd1cf had already added the new first argument, aggstate.

6. Commit 9bdb300 in src/backend/executor/nodeAgg.c added handling for
   parallel workers in the ExecEndAgg function. The earlier commit 6b0e52b
   moved most of the code to the ExecEagerFreeAgg function.

7. Commit 9bdb300 in src/backend/executor/nodeAgg.c added new functions
   ExecAggEstimate, ExecAggInitializeDSM, ExecAggInitializeWorker and
   ExecAggRetrieveInstrumentation, while earlier commits 6195b96 and
   a759b72 had already added functions ExecSquelchAgg and ReuseHashTable
   and others to the same place.