Fixes this test failure:
LinkAll.CommonLinkAllTest
[FAIL] TypeConverter_Custom : ConverterTypeName
String lengths are both 88. Strings differ at index 43.
Expected: "...nk all, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null"
But was: "...nk all, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null"
------------------------------^
at LinkAll.CommonLinkAllTest.TypeConverter_Custom() in /Users/rolf/work/maccore/whatever/xamarin-macios/tests/linker/CommonLinkAllTest.cs:line 88
Fixes this test failure:
LinkAll.CommonLinkAllTest
[FAIL] TypeConverter_BuiltIn : ConverterTypeName
Expected string length 113 but was 142. Strings differ at index 46.
Expected: "...Model.BooleanConverter, System, Version=2.0.5.0, Culture=n..."
But was: "...Model.BooleanConverter, System.ComponentModel.TypeConverte..."
--------------------------------------------^
at LinkAll.CommonLinkAllTest.TypeConverter_BuiltIn() in /Users/rolf/work/maccore/whatever/xamarin-macios/tests/linker/CommonLinkAllTest.cs:line 79
Existing binding binaries won't have the `[Preserve]` attribute on
the `Handler` field and, with the new optimization, would not work
properly.
This tweak make sure that older, already linker-safe, bindings will
remain this way (safe) in this (and future) versions of both iOS and
macOS SDK.