Provide initialization of all fields of type Standard_Real (double) in classes (start from gp)

As it is discovered (see bugs OCC21810 and RLN's fix #0000410 in OCC21843),
uninitialized double-valued fields in classes can cause problems in runtime
even if by the code they are not used until initialized, when such class is
copied (e.g. added to collection):

- Exception may happen (see OCC21810)

- Memory checker will complain on uninitialized memory access (RLN fix)

The only regular way to avoid this problem is to provide initialization of all
fields having type double. In OCCT it refers first of all to classes in gp
package, other should be considered later.