Powershell TSP support

**Background**

After we migrate to TypeSpec, there will be only one swagger. In the storage's case, there are multiple swagger files. They generate powershell code from part of these swaggers, not all of these swagger files.

**Consideration**
We might ask powershell to support tsp input, or maybe provide other solutions.

Start by reading the issue's background about migrating to TypeSpec, multiple storage Swagger files, and generating PowerShell from only part of them. The issue names no files, tests, or entry points and leaves the solution open, so done is not yet defined.

Written by the indexing model from the issue text.