Decide and implement usage of InheritanceKeyValueStore

[farhan]

Video Block is using InheritanceKeyValueStore in parse_xml method

In extracted Video Block we have copy pasted (for the time beign to avoid blocker) the InheritanceKeyValueStore class definition from inheritance.py of edx-platform to video_utils.py of extracted video block.

In this story we will explore its history (purpose of definition) and will take decision on its usage.

One option could be to move it to xblock upstream so both edx-platform and xblocks-contrib/video use same class.

Following test case is failing because of this class difference, fix it within the scope of this story.
xmodule/tests/test_import.py::ImportTestCase::test_metadata_inherit

Relevant test cases PR: openedx/edx-platform#37851

[farhan]

@kdmccormick @feanil
Please share thoughts on this ticket

[feanil]

I think given that this builds on top of the KeyValueStore from the xblock library, and is meant to be generic, we should just move the InheritanceKeyValueStore definition up to the XBlock library.

[farhan]

InheritanceKeyValueStore usage has been removed by updating parse_xml method in the Extracted Video Block class.
Thanks to @ttqureshi for helping in it.

https://github.com/openedx/xblocks-contrib/pull/83/files#diff-f2ca8c95b7d705ded56fd5a55b56aecfd74fe267c097d058e517735bd273a933R637

Extracted Video Block code cleaning (isort imports, some pylint fixes) has also been done in scope of this PR.