Realm backend

[chenzhuofu]

Description of changes:
Realm backend implementation.

Related Issues:

Linked Issues:

• Issue #

Issues closed by this PR:

• Closes #

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This change is 

[codecov]

Codecov Report

Attention: Patch coverage is 18.25168% with 851 lines in your changes missing coverage. Please review.

Project coverage is 58.12%. Comparing base (2b71235) to head (2c0b573).
Report is 5 commits behind head on master.

Files with missing lines	Patch %	Lines
lib/local-execution/src/local_training_backing.cc	0.00%	116 Missing ⚠️
lib/local-execution/src/optimizer.cc	0.00%	103 Missing ⚠️
lib/local-execution/src/loss_functions.cc	0.00%	83 Missing ⚠️
lib/local-execution/src/local_tensor_backing.cc	41.59%	66 Missing ⚠️
lib/local-execution/src/task_binding.cc	0.00%	56 Missing ⚠️
lib/task-spec/src/op_task_to_task_invocation.cc	0.00%	54 Missing ⚠️
lib/local-execution/src/model_training_instance.cc	0.00%	36 Missing ⚠️
lib/local-execution/src/local_cost_estimator.cc	0.00%	26 Missing ⚠️
.../local-execution/src/generic_task_impl_function.cc	0.00%	23 Missing ⚠️
...cal-execution/src/fwd_bwd_op_task_impl_function.cc	8.69%	21 Missing ⚠️
... and 43 more

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1592      +/-   ##
==========================================
- Coverage   60.90%   58.12%   -2.78%     
==========================================
  Files         620      636      +16     
  Lines       14541    15242     +701     
==========================================
+ Hits         8856     8860       +4     
- Misses       5685     6382     +697     

Flag	Coverage Δ
unittests	58.12% <18.25%> (-2.78%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
lib/kernels/include/kernels/legion_dim.h	0.00% <ø> (-25.00%)	⬇️
lib/kernels/src/allocation.cc	62.50% <100.00%> (ø)
.../include/local-execution/itask_argument_accessor.h	100.00% <ø> (ø)
...ion/include/local-execution/local_cost_estimator.h	0.00% <ø> (ø)
lib/local-execution/src/allocated_tensors.cc	100.00% <100.00%> (ø)
lib/local-execution/src/gradient_tensor_source.cc	100.00% <100.00%> (ø)
...cal-execution/src/local-execution/ops/attention.cc	46.96% <100.00%> (ø)
...b/local-execution/src/local-execution/ops/input.cc	0.00% <ø> (ø)
...ib/local-execution/src/local-execution/ops/noop.cc	0.00% <ø> (ø)
.../local-execution/src/local-execution/ops/weight.cc	0.00% <ø> (ø)
... and 70 more

... and 5 files with indirect coverage changes