[turbofan] Rename --context-specialization to --function-context-specialization.

test/mjsunit/regress/regress-osr-context.js

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// Flags: --allow-natives-syntax --context-specialization --turbo-filter=f
+// Flags: --allow-natives-syntax --function-context-specialization
+// Flags: --turbo-filter=f
 
 (function() {
   "use strict";
   var a = 23;
   function f() {
     for (let i = 0; i < 5; ++i) {
       a--;  // Make sure {a} is non-immutable, hence context allocated.
       function g() { return i }  // Make sure block has a context.
       if (i == 2) %OptimizeOsr();
     }
     return a;
   }
   assertEquals(18, f());
 })();