swift-package-migrate: Hide global options

Currently, options that are specific to `swift package migrate` are
shown at the very bottom, following all the global options.

All anonymous option groups get coalesced into the default "OPTIONS"
section, which always comes last. So there is no proper way to hoist
subcommand options above all the base/global options other than giving
the subcommand option group a title.

Using "options" as the title would give us 2 "OPTIONS" sections, whereas
a custom title, such as "migrate options", would introduce yet another
design inconsistency. Instead, address this by hiding global options, as
most other package subcommands do.

Author: AnthonyLatsis

Sources/Commands/PackageCommands/Migrate.swift

@@ -57,7 +57,7 @@ extension SwiftPackageCommand {
             abstract: "Migrate a package or its individual targets to use the given set of features."
         )
 
-        @OptionGroup()
+        @OptionGroup(visibility: .hidden)
         public var globalOptions: GlobalOptions
 
         @OptionGroup()

Tests/CommandsTests/PackageCommandTests.swift

@@ -2106,6 +2106,15 @@ class PackageCommandTestCase: CommandsBuildProviderTestCase {
         }
     }
 
+    func testMigrateCommandHelp() async throws {
+        let (stdout, _) = try await self.execute(
+            ["migrate", "--help"],
+        )
+
+        // Global options are hidden.
+        XCTAssertNoMatch(stdout, .contains("--package-path"))
+    }
+
     func testMigrateCommand() async throws {
         try XCTSkipIf(
             !UserToolchain.default.supportesSupportedFeatures,