Bitbucket server fixes

Created by: lguychard

This introduces several fixes for Bitbucket server v5.15.1

Related issue: #2917

• Fixes styling of command palette and code view toolbar buttons

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• Adds a "View repository on Sourcegraph" button next to the branch selector / branch actions

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• Fixes code view resolution / code intelligence on branch compare pages

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• Fixes code view resolution / code intelligence on single file "Diff to previous" views

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