Command plugin Xcode extension name fixed (#7277)

Template resulting from `swift package init --type command-plugin` did
not auto generate the extension name and used boilerplate instead.

### Motivation:

Seems like a small oversight, not an intentional difference. 

### Modifications:

InitPackage.swift line 553 goes from `extension MyCommandPlugin:
XcodeCommandPlugin {` to `extension \(typeName): XcodeCommandPlugin {`

### Result:

Template generates correctly.

Author: carlynorama

Sources/Workspace/InitPackage.swift

@@ -550,7 +550,7 @@ public final class InitPackage {
                 #if canImport(XcodeProjectPlugin)
                 import XcodeProjectPlugin
 
-                extension MyCommandPlugin: XcodeCommandPlugin {
+                extension \(typeName): XcodeCommandPlugin {
                     // Entry point for command plugins applied to Xcode projects.
                     func performCommand(context: XcodePluginContext, arguments: [String]) throws {
                         print("Hello, World!")