Performance issue with localizable controls and forms

* .NET Core Version: .NT Core 3.0 GA
* Have you experienced this same bug with .NET Framework?: No

**Problem description:**
Right now switching the Localizable property on control causes a large amount of properties moved to a .resx file. At runtime this is loaded with heavy use of reflection and deserialization which shows up in our performance profiles as the biggest reason for slow startup time. In our scenario all the controls and forms are designed using flexible layout containers that are automatically sized to fit the text. The all-or-nothing approach to localization, however, causes the control locations and sizes to be moved to .resx file as well. This results in unnecessarily high number of resources that we never localize and that also cause unnecessary re-layouts at startup.