Fixed a few issues from MFE Bugbash India sheet

[vivek-harness]

https://docs.google.com/spreadsheets/d/1kaR5TYxFxE6esk2JxO5VJdPVPFWHtVW7efQ5ZdTK7Go/edit?pli=1&gid=472839805#gid=472839805

This PR fixes the following issues from the above sheet:

• Clicking on Repoisitories in breadcrumbs navigates to incorrect path
• Change branch -> Click on "xx commits behind" -> 404 page
• Commit details page throwing 404 when navigated from commits page
• While using Light Theme, monaco editor highlights file changes in black background color
• In Light theme, open pull request count is shown in white color, and hence it seems to not exist
• MFE: PR compare - changes - diff view has black background in light theme
• MFE : click on repo name in breadcrumb navigates to wrong path

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