[vm/ffi] Roll package:ffi to Allocator and Opaque

This can only be landed when `Allocator` and `Opaque` have rolled into
Flutter/engine, that into Flutter/flutter, and that into g3.
flutter/flutter/commit/a706cd211240f27be3b61f06d70f958c7a4156fe

Deletes all the copies of `_CallocAllocator` and uses the one from
`package:ffi` instead.

Issue: #44622
Issue: #43974
Issue: #44621
Issue: #38721

Change-Id: I50b3b4c31a2b839b35e3e057bd54f463b90bc55e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/179540
Reviewed-by: Aske Simon Christensen <[email protected]>

Author: dcharkes

DEPS

@@ -102,7 +102,7 @@ vars = {
 
   "chromedriver_tag": "83.0.4103.39",
   "dartdoc_rev" : "9e61a4f11091aaa8998525a2692b14148dc24ab5",
-  "ffi_rev": "31352979f261f7c6ea88fa0a2cfb0fdd004c38fb",
+  "ffi_rev": "ad6700de10ca3af16f0c3d9ff8aa15d2bd7cd21c",
   "fixnum_rev": "16d3890c6dc82ca629659da1934e412292508bba",
   "file_rev": "0e09370f581ab6388d46fda4cdab66638c0171a1",
   "glob_rev": "7c0ef8d4fa086f6b185c4dd724b700e7d7ad8f79",
@@ -115,7 +115,7 @@ vars = {
   "http_throttle_tag" : "1.0.2",
   "icu_rev" : "79326efe26e5440f530963704c3c0ff965b3a4ac",
   "idl_parser_rev": "5fb1ebf49d235b5a70c9f49047e83b0654031eb7",
-  "intl_tag": "0.17.0-nullsafety",
+  "intl_tag": "ade5a936a1de62e7cd04c3ea956c02bd491d7868",
   "jinja2_rev": "2222b31554f03e62600cd7e383376a7c187967a1",
   "json_rpc_2_rev": "b8dfe403fd8528fd14399dee3a6527b55802dd4d",
   "linter_tag": "0.1.128",

benchmarks/FfiBoringssl/dart/FfiBoringssl.dart

@@ -11,7 +11,6 @@ import 'dart:typed_data';
 import 'package:benchmark_harness/benchmark_harness.dart';
 import 'package:ffi/ffi.dart';
 
-import 'calloc.dart';
 import 'digest.dart';
 import 'types.dart';
 

benchmarks/FfiBoringssl/dart/calloc.dart

@@ -13,7 +13,6 @@ import 'dart:typed_data';
 import 'package:benchmark_harness/benchmark_harness.dart';
 import 'package:ffi/ffi.dart';
 
-import 'calloc.dart';
 import 'digest.dart';
 import 'types.dart';
 

benchmarks/FfiBoringssl/dart2/FfiBoringssl.dart

@@ -13,7 +13,6 @@ import 'dart:io';
 import 'package:ffi/ffi.dart';
 import 'package:benchmark_harness/benchmark_harness.dart';
 
-import 'calloc.dart';
 import 'dlopen_helper.dart';
 
 //

benchmarks/FfiBoringssl/dart2/calloc.dart

@@ -15,7 +15,6 @@ import 'dart:io';
 import 'package:ffi/ffi.dart';
 import 'package:benchmark_harness/benchmark_harness.dart';
 
-import 'calloc.dart';
 import 'dlopen_helper.dart';
 
 //