[WIP][dotnet][linker] Enable the sealer optimization

when (by default)
* the interpreter is not enabled (since new code might subclass or override the members analyzed at build time)
* building for release

Reverts c56b893
Fix #9573

Work-in-progress:
* should be made easier to enable/disable (from user projects)
* the above conditions should be the default (if nothing is specified)

dotnet/targets/Xamarin.Shared.Sdk.targets

@@ -302,6 +302,9 @@
 			-->
 			<_ExtraTrimmerArgs>$(_ExtraTrimmerArgs) --disable-opt unusedtypechecks</_ExtraTrimmerArgs>
 
+			<!-- if a release build, not using the JIT (macOS) or the interpreter then the sealer optimization can be used -->
+			<_ExtraTrimmerArgs Condition="'$(_BundlerDebug)' != 'true' And '$(MtouchInterpreter)' == '' And '$(_PlatformName)' != 'macOS'">$(_ExtraTrimmerArgs) --enable-opt sealer</_ExtraTrimmerArgs>
+
 			<!-- We always want the linker to process debug symbols, even when building in Release mode, because the AOT compiler uses the managed debug symbols to output DWARF debugging symbols -->
 			<TrimmerRemoveSymbols Condition="'$(TrimmerRemoveSymbols)' == ''">false</TrimmerRemoveSymbols>
 		</PropertyGroup>

tests/linker/ios/link all/SealerTest.cs

@@ -36,9 +36,6 @@ public class Subclass : Base, Interface {
 	[Preserve (AllMembers = true)]
 	public class SealerTest {
 
-#if !DEBUG && NET
-		[Ignore ("https://github.com/xamarin/xamarin-macios/issues/9573")]
-#endif
 		[Test]
 		public void Sealed ()
 		{
@@ -62,9 +59,6 @@ public void Sealed ()
 #endif
 		}
 
-#if !DEBUG && NET
-		[Ignore ("https://github.com/xamarin/xamarin-macios/issues/9573")]
-#endif
 		[Test]
 		public void Final ()
 		{
@@ -85,9 +79,6 @@ public void Final ()
 #endif
 		}
 
-#if !DEBUG && NET
-		[Ignore ("https://github.com/xamarin/xamarin-macios/issues/9573")]
-#endif
 		[Test]
 		public void Virtual ()
 		{