STYLE: Ensure that ContinuousIndex TCoordRep is a floating point type
STYLE: Ensure that ContinuousIndex TCoordRep is a floating point type

In order for `ContinuousIndex<TCoordRep>` to represent a continuous
index, `TCoordRep` must be a floating point type. This commit checks
this requirement at compile-time, and replaces an unsafe function-style
cast by `static_cast<TCoordRep>`.

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