getPointerPosition returns wrong position if the container is transformed

[vakarelov]

Description

Briefly describe the issue.
The algorithm of getPointerPosition assumes that video container is not subject to scaling and rotation transformations. As a result, it produces the wrong value what such transformations exist.

Steps to reproduce

Explain in detail the exact steps necessary to reproduce the issue.

1. Add the video container in a div that has a transformation. See attached file
   video_test.zip

2. The slider does not provide correct position

#version: 7.7.5

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[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[gkatsev]

Yeah, there's definitely an issue and there is a PR that needs to be fixed up that addresses this #5773