Designer removes needed code

* .NET Core Version:
TargetFramework: net5.0-windows
SDKs: 6.0.100-rc.1.21463.6, 5.0.401

* Have you experienced this same bug with .NET Framework?: Haven't tried

**Problem description:**

When I try to edit a control from the designer. The designer will remove needed parts of the code from `*.Designer.cs` which results in run-time errors.

**Expected behavior:**

Designer doesn't remove necessary code.

**Minimal repro:**

1. Open control in designer
2. Edit a property

Designer removed the assignment of two fields resulting in NullReferenceExceptions at run-time.

[Video](https://user-images.githubusercontent.com/1784452/135894102-8e47abf4-5d00-4e2b-970a-21d8d9f236e3.mp4)

[Code](https://github.com/MisinformedDNA/winforms-designer-issue)

~[Code after designer changes](https://github.com/MisinformedDNA/winforms-designer-issue/tree/actual)~ [New after changes](https://github.com/MisinformedDNA/winforms-designer-issue/commit/f4a84b98fa151f05250a3df0155105edf598fbfb)

NOTE: I inherited this code and have never used the designer on this control before, so maybe something the `designer.cs` or `resx` files are invalid in some way?

dotnet --info

> ❯ dotnet --info
> .NET SDK (reflecting any global.json):
> Version:
> Commit: e627d556a1
>
> Runtime Environment:
> OS Name: Windows
> OS Version: 10.0.18363
> OS Platform: Windows
> RID: win10-x64
> Base Path: C:\Program Files\dotnet\sdk\6.0.100-rc.1.21463.6\
>
> Host (useful for support):
> Version: 6.0.0-rc.1.21451.13
> Commit: d7619cd4b1
>
> .NET SDKs installed:
> 3.1.409 [C:\Program Files\dotnet\sdk]
> 5.0.400 [C:\Program Files\dotnet\sdk]
> 5.0.401 [C:\Program Files\dotnet\sdk]
> 6.0.100-rc.1.21463.6 [C:\Program Files\dotnet\sdk]
>
> .NET runtimes installed:
> Microsoft.AspNetCore.All 2.1.29 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
> Microsoft.AspNetCore.App 2.1.29 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
> Microsoft.AspNetCore.App 3.1.15 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
> Microsoft.AspNetCore.App 3.1.18 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
> Microsoft.AspNetCore.App 3.1.19 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
> Microsoft.AspNetCore.App 5.0.9 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
> Microsoft.AspNetCore.App 5.0.10 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
> Microsoft.AspNetCore.App 6.0.0-rc.1.21452.15 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
> Microsoft.NETCore.App 2.1.29 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
> Microsoft.NETCore.App 3.1.10 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
> Microsoft.NETCore.App 3.1.15 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
> Microsoft.NETCore.App 3.1.18 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
> Microsoft.NETCore.App 3.1.19 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
> Microsoft.NETCore.App 5.0.9 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
> Microsoft.NETCore.App 5.0.10 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
> Microsoft.NETCore.App 6.0.0-rc.1.21451.13 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
> Microsoft.WindowsDesktop.App 3.1.10 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
> Microsoft.WindowsDesktop.App 3.1.13 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
> Microsoft.WindowsDesktop.App 3.1.15 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
> Microsoft.WindowsDesktop.App 3.1.18 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
> Microsoft.WindowsDesktop.App 3.1.19 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
> Microsoft.WindowsDesktop.App 5.0.9 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
> Microsoft.WindowsDesktop.App 5.0.10 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
> Microsoft.WindowsDesktop.App 6.0.0-rc.1.21451.3 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
>