Adding division operators to `Point_` class.

Performs element-wise division.
Adding element-wise division operators to Point3_ class.
Updating documentation to reflect division operations.
Fixed GStreamer encoding pipeline frame drop for most cases.

For several muxers and encoders GStreamer still drops the last frame.
Merge pull request #3252 from GravityJack:point-division
Fixed compatibility with GStreamer 1.x.
More accurate selection of color space conversion element for GStreamer 1.x
Merge pull request #3253 from asmorkalov:ocv_gstreamer2
Correction of the integer data treated as floating point data bug, already corrected in the 2.4 branch.
Neon optimization of cv::scaleAdd (CV_32F)
Merge pull request #3259 from ilya-lavrenov:neon_scale_add_f32
Merge pull request #3257 from Atanahel:gbt_bugfix_master