Add shell integration support for PowerShell

[heaths]

What do you want to change?

I want to add shell integration support similar to what's supported in bash. This would done in similar fashion by setting up $function:prompt (similar to $PS1) and $function:PSConsoleHostReadLine (similar to $PS0).

Why do you want to make this change?

PowerShell (pwsh) is used by many, and I have a lot of experience developing for PowerShell. I use bash more on linux and macOS, but still find myself in PowerShell often enough. I do use oh-my-posh with shell integration and have already submitted some changes to make it work better with Ghostty, but adding support directly in Ghostty would work more generally.

I acknowledge that:

• I have read the Contributing Guide and understand the contribution process.
• I have read and agree to follow the AI Usage Policy.
• I wrote this vouch request myself, in my own voice, without AI generating it.

[jcollie]

!vouch