Use idiomatic Kotlin in Request.kt (#5092)

- define @get:JvmName(...) for the following vals in constructor instead of passing builder: Builder.
  - url: HttpUrl
  - method: String
  - headers: Headers
  - body: RequestBody?

- add @Deprecated(...) to the following functions.
  - fun url(): HttpUrl
  - fun method(): String
  - fun headers(): Headers
  - fun body(): RequestBody?
  - fun cacheControl(): CacheControl

- clean up code where ()(Parentheses) is unnecessarily used.

okhttp-urlconnection/src/main/java/okhttp3/JavaNetAuthenticator.kt

@@ -30,7 +30,7 @@ class JavaNetAuthenticator : okhttp3.Authenticator {
   override fun authenticate(route: Route?, response: Response): Request? {
     val challenges = response.challenges()
     val request = response.request()
-    val url = request.url()
+    val url = request.url
     val proxyAuthorization = response.code() == 407
     val proxy = route?.proxy() ?: Proxy.NO_PROXY