Code review for extracted discussion xblock #495

The purpose of this ticket is to track the code review of multiple PRs related to the extracted Discussion block.

Extracted Discussion Xblock PRs:

• Lift and Shift all code: Discussion xblock extraction from edx-platform xblocks-core#134
• Add discussion service for permission and provider settings: Add discussion service to access permission and access provider xblocks-core#147
• Bundling all JS files with webpack: Discussion XBlock: Bundle up all JS files with webpack xblocks-core#155
• JavaScript (Karma) tests for extracted block: Discussion XBlock: Javascript (karma) tests xblocks-core#163
• Allow tests for Extracted & Builtin Discussion XBlock PR: Allow tests for Extracted & Builtin Discussion XBlock openedx-platform#37875