API: Introducing complex (np.complex64/128) native support

[mloubout]

Support complex float data type.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 82.98755% with 41 lines in your changes missing coverage. Please review.

Project coverage is 86.74%. Comparing base (e37d6ff) to head (b85a70f).

Files	Patch %	Lines
tests/test_gpu_common.py	7.69%	12 Missing :warning:
devito/symbolics/printer.py	61.53%	7 Missing and 3 partials :warning:
devito/passes/iet/dtypes.py	72.72%	6 Missing and 3 partials :warning:
devito/symbolics/inspection.py	81.81%	1 Missing and 1 partial :warning:
tests/test_operator.py	87.50%	1 Missing and 1 partial :warning:
devito/arch/compiler.py	75.00%	1 Missing :warning:
devito/finite_differences/differentiable.py	50.00%	1 Missing :warning:
devito/ir/iet/visitors.py	95.23%	1 Missing :warning:
devito/passes/iet/langbase.py	80.00%	1 Missing :warning:
devito/passes/iet/languages/CXX.py	90.00%	0 Missing and 1 partial :warning:
... and 1 more

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #2375 +/- ## ========================================== - Coverage 86.78% 86.74% -0.04% ========================================== Files 234 237 +3 Lines 44271 44433 +162 Branches 8184 8212 +28 ========================================== + Hits 38419 38543 +124 - Misses 5137 5165 +28 - Partials 715 725 +10 ```

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