Remove TerminalAzBridge and use AzureConnection directly (#19528)

We used to run the cloud shell connector in an intermediate process
because our VT implementation lived mostly in conhost. James fixed that
up over the intervening years, and since #17510 landed Terminal is
exposed to 100% of application-originated VT. That means we no longer
need this workaround, its build steps, or anything else about it.

Closes #4661

(cherry picked from commit 4b946c0d5cc0264ff0529643f9455fd2c6c227b4)
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