Add new Handle constructor for easier initialization

[saikishor]

Right now, when we add new tests, we will have to generate the InterfaceInfo for each state and command interface, and this is nothing but increasing the lines of code. I've added a new constructor that we can use inside the tests

Previous approach

  const std::string collision_interface = "collision";
  const std::string itf_name = "joint1";
  InterfaceInfo info;
  info.name = collision_interface;
  info.data_type = "bool";
  InterfaceDescription interface_descr(itf_name, info);
  StateInterface handle{interface_descr};

New approach:

  const std::string POSITION_INTERFACE = "position";
  const std::string JOINT_NAME_1 = "joint1";
  StateInterface handle{itf_name, POSITION_INTERFACE, "double", "23.0"};

[codecov]

Codecov Report

Attention: Patch coverage is 87.50000% with 4 lines in your changes missing coverage. Please review.

Project coverage is 88.92%. Comparing base (7f0bd68) to head (d123216).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
...re_interface/include/hardware_interface/handle.hpp	89.47%	2 Missing ⚠️
hardware_interface/test/test_handle.cpp	83.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2253      +/-   ##
==========================================
- Coverage   88.92%   88.92%   -0.01%     
==========================================
  Files         143      143              
  Lines       16436    16454      +18     
  Branches     1422     1422              
==========================================
+ Hits        14615    14631      +16     
- Misses       1268     1270       +2     
  Partials      553      553              

Flag	Coverage Δ
unittests	88.92% <87.50%> (-0.01%)	⬇️

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

Files with missing lines	Coverage Δ
...rface/include/hardware_interface/hardware_info.hpp	81.48% <100.00%> (+0.71%)	⬆️
...re_interface/include/hardware_interface/handle.hpp	90.90% <89.47%> (-0.27%)	⬇️
hardware_interface/test/test_handle.cpp	98.48% <83.33%> (-1.52%)	⬇️

... and 2 files with indirect coverage changes

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[christophfroehlich]

LGTM, some minor requests only