Add view on code host for Bitbucket Cloud

Created by: artemruts

Description

While doing a walkthrough with a customer @emchap noticed that we can't navigate from Sourcegraph to Bitbucket Cloud.

Changes

This PR:

• Adds View on Bitbucket Cloud button to let users navigate from Sourcegraph to Bitbucket Cloud
• Adds support for links with range or position for Bitbucket Cloud and Bitbucket Server

Tested

Since I touched the range and position logic a bit, I tested on repositories from:

• GitHub
• GitLab
• Bitbucket Server (https://bitbucket.sgdev.org/)
• Bitbucket Cloud (https://bitbucket.org/)

Notes

1. @quinnkeast Customer shared that the Bitbucket icon looks a bit like delete button. What could we do about this?
2. I didn't add the compare/diff link functionality yet but can make another ticket and add it for Bitbucket (I think .org supports it)