[dotnet] Stop suppressing trim analysis warnings. Fixes #21293. (#21351)

Our own code shouldn't produce trim analysis warnings anymore (see #10405), so we don't need to suppress trim analysis warnings for everyone. 

Except: we still want to suppress trim analysis warnings if no assemblies are trimmed,  because otherwise we'll get warnings for code that would otherwise be trimmed away.

On the other hand, we want trim analyzer always enabled, so that warnings are reported for user code.

The difference between "trim analyzer" and "trim analysis warnings" is that the former is an analyzer that analyzes the currently compiled code (which we always want), while the latter is reported by the trimmers, and as such will report warnings from *all* code, including all references.

This also required bumping Touch.Unit and MonoTouch.Dialog.

* New commits in xamarin/MonoTouch.Dialog:

    * xamarin/MonoTouch.Dialog@d157950 Exclude code that's not trimmer safe.

        Diff: [77b3337..d157950](https://github.com/xamarin/MonoTouch.Dialog/compare/77b3337dbbc9e3e2f1b06dab3d37d2822488b0b3..d157950b6e6ed32cf53d4074fe19223dc1f1e8fe)

* New commits in xamarin/Touch.Unit:

    * xamarin/Touch.Unit@957faca [Touch.Client] Disable features that aren't trimmer safe.

        Diff: [92a0726..957faca](https://github.com/xamarin/Touch.Unit/compare/92a072683b69b2f61f235a7a249c2c7f261236d4..957facad80e753310f52fcbb8cf85219d9d6d887)

Fixes #21293.

dotnet/targets/Xamarin.Shared.Sdk.Trimming.props

@@ -81,9 +81,12 @@
 		-->
 		<_OriginalSuppressTrimAnalysisWarnings>$(SuppressTrimAnalysisWarnings)</_OriginalSuppressTrimAnalysisWarnings>
 		<SuppressTrimAnalysisWarnings Condition="'$(_UseNativeAot)' == 'true'">true</SuppressTrimAnalysisWarnings>
-		<!-- Otherwise suppress trimmer warnings unless we're trimming all assemblies -->
-		<SuppressTrimAnalysisWarnings Condition="'$(SuppressTrimAnalysisWarnings)' == '' And '$(TrimMode)' == 'full'">false</SuppressTrimAnalysisWarnings>
-		<SuppressTrimAnalysisWarnings Condition="'$(SuppressTrimAnalysisWarnings)' == '' And '$(PublishAot)' == 'true'">false</SuppressTrimAnalysisWarnings>
-		<SuppressTrimAnalysisWarnings Condition="'$(SuppressTrimAnalysisWarnings)' == ''">true</SuppressTrimAnalysisWarnings>
+
+		<!-- Otherwise only suppress trimmer warnings if we're not actually trimming any assemblies. -->
+		<SuppressTrimAnalysisWarnings Condition="'$(SuppressTrimAnalysisWarnings)' == '' And '$(TrimMode)' == 'copy'">true</SuppressTrimAnalysisWarnings>
+		<SuppressTrimAnalysisWarnings Condition="'$(SuppressTrimAnalysisWarnings)' == '' And '$(TrimMode)' != 'copy'">false</SuppressTrimAnalysisWarnings>
+
+		<!-- Always enable trim analyzers. This will report problems in code that's compiled, but not in any referenced packages / NuGets / projects, etc. -->
+		<EnableTrimAnalyzer Condition="'$(EnableTrimAnalyzer)' == ''">true</EnableTrimAnalyzer>
 	</PropertyGroup>
 </Project>

tests/common/shared-dotnet.csproj

@@ -81,6 +81,8 @@
 		<TrimmerSingleWarn Condition="'$(TrimmerSingleWarn)' == ''">false</TrimmerSingleWarn>
 		<!-- IL2104: Assembly '...' produced trim warnings -->
 		<NoWarn>$(NoWarn);IL2104</NoWarn>
+		<!-- Touch.Unit is not trimmer-safe, so ignore any trimmer warnings if we're including Touch.Unit in the build -->
+		<SuppressTrimAnalysisWarnings Condition="'$(SuppressTrimAnalysisWarnings)' == '' And '$(ExcludeTouchUnitReference)' != 'true'">true</SuppressTrimAnalysisWarnings>
 	</PropertyGroup>
 	<Target Name="IgnoreTrimmerWarningsInNUnit" BeforeTargets="PrepareForILLink">
 		<ItemGroup>