Remove inline from PointTransform methods to be exported

When PointTransform was converted to the new filter structure, some of the methods that were moved from .hxx to .cxx (and therefore compiled in a library) were still marked as inline. This caused the compiler to not compile the function into the library if it was not used. Fix the problem by removing the inline modifier to the method implementations.

Fixes: #697 (closed)

Backport: release