Fix compilation error in drawRefAxis function

[traversaro]

In some platforms, you can't have an implicit narrowing cast in inizializer lists, unless the argument is constant. Before this PR, the code resulted in this error:

2022-02-14T19:54:21.2244330Z /Users/runner/work/robotology-superbuild/robotology-superbuild/src/event-driven/lib/src/vIPT.cpp:493:31: error: non-constant-expression cannot be narrowed from type 'double' to 'float' in initializer list [-Wc++11-narrowing]
2022-02-14T19:54:21.2346020Z     std::array<float, 3> r = {a*x, a*y, a*z};
2022-02-14T19:54:21.2446960Z                               ^~~
2022-02-14T19:54:21.2548470Z /Users/runner/work/robotology-superbuild/robotology-superbuild/src/event-driven/lib/src/vIPT.cpp:493:31: note: insert an explicit cast to silence this issue
2022-02-14T19:54:21.2649640Z     std::array<float, 3> r = {a*x, a*y, a*z};
2022-02-14T19:54:21.2750520Z                               ^~~
2022-02-14T19:54:21.2851510Z                               static_cast<float>( )
2022-02-14T19:54:21.2945990Z /Users/runner/work/robotology-superbuild/robotology-superbuild/src/event-driven/lib/src/vIPT.cpp:493:36: error: non-constant-expression cannot be narrowed from type 'double' to 'float' in initializer list [-Wc++11-narrowing]
2022-02-14T19:54:21.3052730Z     std::array<float, 3> r = {a*x, a*y, a*z};
2022-02-14T19:54:21.3153570Z                                    ^~~
2022-02-14T19:54:21.3255100Z /Users/runner/work/robotology-superbuild/robotology-superbuild/src/event-driven/lib/src/vIPT.cpp:493:36: note: insert an explicit cast to silence this issue
2022-02-14T19:54:21.3356110Z     std::array<float, 3> r = {a*x, a*y, a*z};
2022-02-14T19:54:21.3456980Z                                    ^~~
2022-02-14T19:54:21.3558010Z                                    static_cast<float>( )
2022-02-14T19:54:21.3659480Z /Users/runner/work/robotology-superbuild/robotology-superbuild/src/event-driven/lib/src/vIPT.cpp:493:41: error: non-constant-expression cannot be narrowed from type 'double' to 'float' in initializer list [-Wc++11-narrowing]
2022-02-14T19:54:21.3760690Z     std::array<float, 3> r = {a*x, a*y, a*z};
2022-02-14T19:54:21.3860890Z                                         ^~~
2022-02-14T19:54:21.3962540Z /Users/runner/work/robotology-superbuild/robotology-superbuild/src/event-driven/lib/src/vIPT.cpp:493:41: note: insert an explicit cast to silence this issue
2022-02-14T19:54:21.4062140Z     std::array<float, 3> r = {a*x, a*y, a*z};
2022-02-14T19:54:21.4163080Z                                         ^~~
2022-02-14T19:54:21.4264100Z                                         static_cast<float>( )
2022-02-14T19:54:21.4364440Z 12 warnings and 3 errors generated.

Fix robotology/robotology-superbuild#1033 .

[traversaro]

In some platforms

After a few more check "in some platforms" is actually macOS/clang.

[traversaro]

fyi @arrenglover

[arrenglover]

thanks @traversaro