define_property(): Clean up docs and implementation related to INITIALIZE_FROM_VARIABLE

INITIALIZE_FROM_VARIABLE is new in CMake 3.23, but the versionadded note was missing in the original commit. The docs also failed to mention that the new option only applies to target properties. The docs for define_property() also no longer reflected what the command was mostly useful for, so they have been updated in line with the comment in #20698 (comment 1109450). A minor code tweak has also been made to avoid an unnecessary argument check when INITIALIZE_FROM_VAFRIABLE is not given.

Backport: release