Pass the -dump-ast-format flag down to the frontend.

Companion PR to swiftlang/swift#77321.

Author: allevato

Sources/SwiftDriver/Jobs/FrontendJobHelpers.swift

@@ -283,6 +283,9 @@ extension Driver {
     try commandLine.appendLast(.lto, from: &parsedOptions)
     try commandLine.appendLast(.accessNotesPath, from: &parsedOptions)
     try commandLine.appendLast(.enableActorDataRaceChecks, .disableActorDataRaceChecks, from: &parsedOptions)
+    if isFrontendArgSupported(.dumpAstFormat) {
+      try commandLine.appendLast(.dumpAstFormat, from: &parsedOptions)
+    }
     try commandLine.appendAll(.D, from: &parsedOptions)
     try commandLine.appendAll(.debugPrefixMap, .coveragePrefixMap, .filePrefixMap, from: &parsedOptions)
     try commandLine.appendAllArguments(.Xfrontend, from: &parsedOptions)

Tests/SwiftDriverTests/SwiftDriverTests.swift

@@ -5561,6 +5561,17 @@ final class SwiftDriverTests: XCTestCase {
     }
   }
 
+  func testDumpASTFormat() throws {
+    var driver = try Driver(args: [
+      "swiftc", "-dump-ast", "-dump-ast-format", "json", "foo.swift"
+    ])
+    let plannedJobs = try driver.planBuild()
+    XCTAssertEqual(plannedJobs[0].kind, .compile)
+    XCTAssertTrue(plannedJobs[0].commandLine.contains("-dump-ast"))
+    XCTAssertTrue(plannedJobs[0].commandLine.contains("-dump-ast-format"))
+    XCTAssertTrue(plannedJobs[0].commandLine.contains("json"))
+  }
+
   func testDeriveSwiftDocPath() throws {
     var driver = try Driver(args: [
       "swiftc", "-emit-module", "/tmp/main.swift", "-emit-module-path", "test-ios-macabi.swiftmodule"