Pass through swift-testing's experimental JSON streams from swift test (#7534)

This PR adds two undocumented/unsupported experimental options to `swift
test` to allow passing through JSON files/streams for input and output.
These streams are still under development in swift-testing, so these
options are not yet supported, but this change will allow interested
coders to experiment with them.

---------

Co-authored-by: Max Desiatov <m_desiatov@apple.com>

Author: grynspan

Sources/Commands/SwiftTestCommand.swift

@@ -154,6 +154,16 @@ struct TestCommandOptions: ParsableArguments {
     var enableExperimentalTestOutput: Bool {
         return testOutput == .experimentalSummary
     }
+
+    /// Path where swift-testing's JSON configuration should be read.
+    @Option(name: .customLong("experimental-configuration-path"),
+            help: .hidden)
+    var configurationPath: AbsolutePath?
+
+    /// Path where swift-testing's JSON output should be written.
+    @Option(name: .customLong("experimental-event-stream-output"),
+            help: .hidden)
+    var eventStreamOutputPath: AbsolutePath?
 }
 
 /// Tests filtering specifier, which is used to filter tests to run.
@@ -688,9 +698,10 @@ extension SwiftTestCommand {
                 sanitizers: globalOptions.build.sanitizers
             )
 
+            let additionalArguments = ["--list-tests"] + CommandLine.arguments.dropFirst()
             let runner = TestRunner(
                 bundlePaths: testProducts.map(\.binaryPath),
-                additionalArguments: ["--list-tests"],
+                additionalArguments: additionalArguments,
                 cancellator: swiftCommandState.cancellator,
                 toolchain: toolchain,
                 testEnv: testEnv,