Random Crashes with ns7 core modules

从 app/packages/core/ui/core/view/index.ios.ts 中的 _removeViewFromNativeVisualTree 开始，沿着经过 view-base/index.ts 和 layout-base-common.ts 的 teardown 调用进行跟踪。使用报告中的 NativeScript 7 和 Xcode 12 配置在 iOS 设备上复现该 assertion，然后确认在观察到的条件下 teardown 路径不再崩溃。

We're also experiencing pretty random but often crash from time to time on iOS devices with latest NS 7 core modules and the project built with Xcode 12:

====== Assertion failed ======
Native stack trace:
1          0x1019f4f3c tns::Assert(bool, v8::Isolate*) + 128
2          0x10196178c tns::ArgConverter::Invoke(v8::Local<v8::Context>, objc_class*, v8::Local<v8::Object>, tns::V8Args&, tns::MethodMeta const*, bool) + 100
3          0x1019ba984 tns::MetadataBuilder::InvokeMethod(v8::Local<v8::Context>, tns::MethodMeta const*, v8::Local<v8::Object>, tns::V8Args&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, bool) + 88
4          0x1019ba210 tns::MetadataBuilder::MethodCallback(v8::FunctionCallbackInfo<v8::Value> const&) + 220
5          0x101b23e10 v8::internal::FunctionCallbackArguments::Call(v8::internal::CallHandlerInfo) + 536
6          0x101b233dc v8::internal::MaybeHandle<v8::internal::Object> v8::internal::(anonymous namespace)::HandleApiCallHelper<false>(v8::internal::Isolate*, v8::internal::Handle<v8::internal::HeapObject>, v8::internal::Handle<v8::internal::HeapObject>, v8::internal::Handle<v8::internal::FunctionTemplateInfo>, v8::internal::Handle<v8::internal::Object>, v8::internal::BuiltinArguments) + 516
7          0x101b22b7c v8::internal::Builtin_Impl_HandleApiCall(v8::internal::BuiltinArguments, v8::internal::Isolate*) + 224
8          0x1022b4d8c Builtins_CEntry_Return1_DontSaveFPRegs_ArgvOnStack_BuiltinExit + 108
9          0x10224d6b4 Builtins_InterpreterEntryTrampoline + 244
10         0x10224d6b4 Builtins_InterpreterEntryTrampoline + 244
11         0x10224d6b4 Builtins_InterpreterEntryTrampoline + 244
12         0x10224d6b4 Builtins_InterpreterEntryTrampoline + 244
13         0x10224d6b4 Builtins_InterpreterEntryTrampoline + 244
14         0x10224d6b4 Builtins_InterpreterEntryTrampoline + 244
15         0x10224d6b4 Builtins_InterpreterEntryTrampoline + 244
16         0x10224d6b4 Builtins_InterpreterEntryTrampoline + 244
17         0x10224d6b4 Builtins_InterpreterEntryTrampoline + 244
18         0x10224d6b4 Builtins_InterpreterEntryTrampoline + 244
19         0x102246504 Builtins_ArgumentsAdaptorTrampoline + 228
20         0x10224d6b4 Builtins_InterpreterEntryTrampoline + 244
21         0x10224d6b4 Builtins_InterpreterEntryTrampoline + 244
22         0x10224d6b4 Builtins_InterpreterEntryTrampoline + 244
23         0x10224d6b4 Builtins_InterpreterEntryTrampoline + 244
24         0x10224af64 Builtins_JSEntryTrampoline + 164
25         0x10224ac08 Builtins_JSEntry + 168
26         0x122ac4000 26  ???                                 0x0000000122ac4000 0x0 + 4876681216
JavaScript stack trace:
at _removeViewFromNativeVisualTree (file: app/packages/core/ui/core/view/index.ios.ts:787:29)
at _tearDownUI (file: app/packages/core/ui/core/view-base/index.ts:871:15)
at <anonymous> (file: app/packages/core/ui/core/view-base/index.ts:865:9)
at eachChildView (file: app/packages/core/ui/layouts/layout-base-common.ts:125:18)
at eachChild (file: app/packages/core/ui/core/view/view-common.ts:867:7)
at _tearDownUI (file: app/packages/core/ui/core/view-base/index.ts:864:7)
at <anonymous> (file: app/packages/core/ui/core/view-base/index.ts:865:9)
at eachChildView (file: app/packages/core/ui/layouts/layout-base-common.ts:125:18)
at eachChild (file: app/packages/core/ui/core/view/view-common.ts:867:7)
at _tearDownUI (file: app/packages/core/ui/core/view-base/index.ts:864:7)

Originally posted by @romandragan in https://github.com/NativeScript/NativeScript/issues/8867#issuecomment-698143588