Use extracted HTML block base for About, StaticTab, CourseInfo

[kdmccormick]

Current state

xblocks-contrib has:

• class HtmlBlock

edx-platform has:

• class HtmlBlockMixin
• class _BuiltinHtmlBlock(HtmlBlockMixin)
• class CourseInfoBlock(HtmlBlockMixin)
• class AboutBlock(HtmlBlockMixin)
• class StaticTabBlock(HtmlBlockMixin)
• HtmlBlock = xblocks-contrib.HtmlBlock if extracted_flag else _BuiltinHtmlBlock

Desired state for rollout

xblocks-contrib has:

• class HtmlBlockMixin
• class HtmlBlock(HtmlBlockMixin)

edx-platform has:

• class _BuiltinHtmlBlockMixin
• class _BuiltinHtmlBlock(_BuiltinHtmlBlockMixin)
• HtmlBlockMixin = xblocks-contrib.HtmlBlockMixin if extracted_flag else _BuiltinHtmlBlockMixin
• class CourseInfoBlock(HtmlBlockMixin)
• class AboutBlock(HtmlBlockMixin)
• class StaticTabBlock(HtmlBlockMixin)
• HtmlBlock = xblocks-contrib.HtmlBlock if extracted_flag else _BuiltinHtmlBlock

Desired final state

xblock-contrib has:

• class HtmlBlockMixin
• class HtmlBlock(HtmlBlockMixin)

edx-platform has:

• class CourseInfoBlock(xblocks-contrib.HtmlBlockMixin)
• class AboutBlock(xblocks-contrib.HtmlBlockMixin)
• class StaticTabBlock(xblocks-contrib.HtmlBlockMixin)

[kdmccormick]

I've assigned you @ttqureshi but feel free to reassign to anyone as appropriate

[feanil]

@ttqureshi I know you're going on leaves soon, @salman2013 can you work with @ttqureshi and pick up this work next if he's unable to get to it?

[salman2013]

@feanil noted, thanks

[salman2013]

PR on edx-platform : #37757
PR on xblocks-contrib: https://github.com/openedx/xblocks-contrib/pull/122/changes