STYLE: Reduce buf size, remove builder.Reset() calls from NumberToString
STYLE: Reduce buf size, remove builder.Reset() calls from NumberToString

Various style improvements of the implementation of the
`NumberToString<TValue>` specializations for floating point numbers:

 - Did clean up the #include's.
 - Removed unnecessary builder.Reset() calls. (`StringBuilder::Reset()` only just sets the internal position to zero, but that is already taken care of by the constructor of `StringBuilder`.)
 - Added local helper function, `FloatingPointNumberToString(val)`, sharing code between `float` and `double` specialization.
 - Reduced size of local buffer (`buf`) from 256 to 32 chars.

Kitware/ITK,thewtex/ITK,thewtex/ITK,vfonov/ITK,InsightSoftwareConsortium/ITK,hjmjohnson/ITK,InsightSoftwareConsortium/ITK,LucasGandel/ITK,BRAINSia/ITK,Kitware/ITK,Kitware/ITK,LucasGandel/ITK,hjmjohnson/ITK,Kitware/ITK,richardbeare/ITK,thewtex/ITK,BRAINSia/ITK,InsightSoftwareConsortium/ITK,richardbeare/ITK,BRAINSia/ITK,BRAINSia/ITK,richardbeare/ITK,vfonov/ITK,InsightSoftwareConsortium/ITK,richardbeare/ITK,richardbeare/ITK,vfonov/ITK,vfonov/ITK,InsightSoftwareConsortium/ITK,BRAINSia/ITK,vfonov/ITK,Kitware/ITK,BRAINSia/ITK,hjmjohnson/ITK,LucasGandel/ITK,LucasGandel/ITK,LucasGandel/ITK,hjmjohnson/ITK,InsightSoftwareConsortium/ITK,hjmjohnson/ITK,richardbeare/ITK,thewtex/ITK,LucasGandel/ITK,thewtex/ITK,thewtex/ITK,vfonov/ITK,hjmjohnson/ITK,LucasGandel/ITK,vfonov/ITK,Kitware/ITK,BRAINSia/ITK,InsightSoftwareConsortium/ITK,vfonov/ITK,hjmjohnson/ITK,Kitware/ITK,richardbeare/ITK,vfonov/ITK,LucasGandel/ITK,thewtex/ITK