[ios] Handle Swift XCTest and XCUITest

It is possible to implement XCTest or XCUITest test cases in Swift,
so update the Xcode project generator to also look for files with
the .swift extension.

Bug: none
Change-Id: I4c657d5a40d3a17c0b3a1f1c8abf90a75a0e78d0
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/12940
Reviewed-by: Petr Hosek <phosek@google.com>
Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>

src/gn/xcode_writer.cc

diff --git a/src/gn/xcode_writer.cc b/src/gn/xcode_writer.cc
index 5e57ec9..c2d8857 100644
--- a/src/gn/xcode_writer.cc
+++ b/src/gn/xcode_writer.cc
@@ -100,7 +100,8 @@
 };
 
 const char* kXCTestFileSuffixes[] = {
-    "egtest.m", "egtest.mm", "xctest.m", "xctest.mm", "UITests.m", "UITests.mm",
+    "egtest.m",     "egtest.mm", "egtest.swift", "xctest.m",      "xctest.mm",
+    "xctest.swift", "UITests.m", "UITests.mm",   "UITests.swift",
 };
 
 const char kXCTestModuleTargetNamePostfix[] = "_module";