Add macros for generating the device entry-point and declarations

[maliasadi]

This PR adds a C++ template macro to facilitate the generation of a device entry-point. For every implementation of QuantumDevice, there are a repeated list of methods declarations in the header file of the class. These declarations can be templated away to reduce the redundant code to write a new backend device. This PR addresses this issue with introducing a couple of macros to generate these declarations. It also updates the signature of extern "C" factory methods to stick to the C data-types.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (7bfe53e) 99.49% compared to head (290d881) 99.49%.

Additional details and impacted files

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  Coverage   99.49%   99.49%           
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  Files          42       42           
  Lines        7150     7150           
  Branches      483      483           
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  Hits         7114     7114           
  Misses         20       20           
  Partials       16       16           

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