Improve domain matching routine per the recommendation on PR.

- Also update unit tests to be more accurate in testing domain matching

Author: maksimorlovich

Foundation/HTTPCookieStorage.swift

@@ -352,8 +352,8 @@ extension HTTPCookie {
         //      domain string is a %x2E (".") character.
         //    * The string is a host name (i.e., not an IP address).
 
-        let dotlessDomain = domain.first == "." ? String(domain.suffix(domain.count - 1)) : domain
-        return dotlessDomain == host || (domain.first == "." && host.hasSuffix(domain))
+        guard domain.hasPrefix(".") else { return host == domain }
+        return host == domain.dropFirst() || host.hasSuffix(domain)
     }
 
     internal func persistableDictionary() -> [String: Any] {

TestFoundation/TestHTTPCookieStorage.swift

@@ -314,11 +314,11 @@ class TestHTTPCookieStorage: XCTestCase {
         let bugsSwiftOrgUrl = URL(string: "https://BUGS.swift.org")!
         let exampleComUrl = URL(string: "http://www.example.com")!
         let superSwiftOrgUrl = URL(string: "https://superswift.org")!
-        XCTAssertEqual(storage.cookies(for: swiftOrgUrl)!.count, 2)
-        XCTAssertEqual(storage.cookies(for: ciSwiftOrgUrl)!.count, 1)
-        XCTAssertEqual(storage.cookies(for: bugsSwiftOrgUrl)!.count, 2)
-        XCTAssertEqual(storage.cookies(for: exampleComUrl)!.count, 0)
-        XCTAssertEqual(storage.cookies(for: superSwiftOrgUrl)!.count, 0)
+        XCTAssertEqual(Set(storage.cookies(for: swiftOrgUrl)!), Set([simpleCookie1, simpleCookie2]))
+        XCTAssertEqual(storage.cookies(for: ciSwiftOrgUrl)!, [simpleCookie2])
+        XCTAssertEqual(Set(storage.cookies(for: bugsSwiftOrgUrl)!), Set([simpleCookie2, simpleCookie3]))
+        XCTAssertEqual(storage.cookies(for: exampleComUrl)!, [])
+        XCTAssertEqual(storage.cookies(for: superSwiftOrgUrl)!, [])
     }
 
     func test_cookieInXDGSpecPath() {