Add a new Log Level called "Verbose"

While working on the PowerShell language worker, I noticed that there's a disconnect in the word choice between what PowerShell calls the log level that is more detailed and what Functions calls it.

* PowerShell calls it "Verbose" and has a command `Write-Verbose`
* Functions calls this level "Trace" and uses that in the host.json

Im afraid this will cause some confusion for our PowerShell customers since the Log Levels wouldn't match up.

Is it possible to support a new Log Level called "Verbose" that acts identically to "Trace"?

Start by tracing how the host.json `Trace` log level is recognized and how the PowerShell language worker uses `Write-Verbose`. Confirm where log-level names are parsed and mapped, then verify that `Verbose` is accepted as an alias with identical behavior to `Trace` and that existing `Trace` behavior remains unchanged.

Written by the indexing model from the issue text.