Update extension and PSES to handle PS Core rename of binary to pwsh

[rkeithhill]

Title says it all. This one will be a bit tricky since we support side-by-side PS Core installations. We can't wholesale change powershell to pwsh - just for PS Core 6.0.0-beta.9 and higher. Do we already have an npm package pulled in that can compare semver v2 versions?

[daviwil]

Maybe just keep it simple and look for either powershell.exe or pwsh.exe in the PowerShell Core install paths?