Move ContextSlotCache to its own file

BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/android/config.gni")
 import("//build/config/arm.gni")
 import("//build/config/dcheck_always_on.gni")
 import("//build/config/mips.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 
@@ skipping 838 matching lines @@
     "src/ast/ast-literal-reindexer.cc",
     "src/ast/ast-literal-reindexer.h",
     "src/ast/ast-numbering.cc",
     "src/ast/ast-numbering.h",
     "src/ast/ast-traversal-visitor.h",
     "src/ast/ast-type-bounds.h",
     "src/ast/ast-value-factory.cc",
     "src/ast/ast-value-factory.h",
     "src/ast/ast.cc",
     "src/ast/ast.h",
+    "src/ast/context-slot-cache.cc",
+    "src/ast/context-slot-cache.h",
     "src/ast/modules.cc",
     "src/ast/modules.h",
     "src/ast/prettyprinter.cc",
     "src/ast/prettyprinter.h",
     "src/ast/scopeinfo.cc",
     "src/ast/scopeinfo.h",
     "src/ast/scopes.cc",
     "src/ast/scopes.h",
     "src/ast/variables.cc",
     "src/ast/variables.h",
@@ skipping 1660 matching lines @@
 
   deps = [
     ":fuzzer_support",
   ]
 
   configs = [ ":internal_config" ]
 }
 
 v8_fuzzer("wasm_asmjs_fuzzer") {
 }