Support multiple connections

[worksofliam]

• Adds the ability to have multiple connections with a single window
• Supports the concept of an 'active connection'
• For backwards compatability, getConnection will always return the first connection. Extensions will need to be updated to use getActiveConnection
• Events fire with the active connection as a parameter
• Generated Uris now require to use the authority property which maps to a connection id.

To do:

• All Uris need to be updated to include the connection name (or host name) as part of the Uri since we can have multiple systems
• Stop the ability to connect to the same system more than once in the UI (you can just keep clicking the Server node)
• New event is needed to fire when the connection is switched
• Add a mode to disable multi-connection mode in the extension, with the feature togglable for those that know what they are doing. We need time to let the extensions to catch up (The db2 extension will need some work to support the new APIs)

[github-actions]

👋 A new build is available for this PR based on 7cebe01.

• Download here.
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