Update PowerShell profile with new custom function

src/powershell/profile.md

@@ -33,4 +33,26 @@ Set-Title-Folder sets the window/tab title, such as for Windows Terminal, based
 #>
 	$Host.UI.RawUI.WindowTitle = Split-Path -Path (Get-Location) -Leaf
 }
+
+function Start-ExtensionOpen {
+<#
+.Description
+Start-ExtensionOpen opens a single file with a matching extension, if possible.
+#>
+	param(
+		[string]
+		$FileExtension
+	)
+	$matchingFiles = Get-ChildItem . -Filter *.$FileExtension
+	$matchCount = ($matchingFiles | Measure-Object).Count
+
+	if ($matchCount -eq 1) {
+		Write-Output "Opening $($matchingFiles.Name)"
+		Invoke-Item $matchingFiles[0]
+	} elseif ($matchCount -eq 0) {
+		Write-Error "No matching files for $($FileExtension)"
+	} else {
+		Write-Output $matchingFiles.Name
+	}
+}
 ```