[Xamarin.Android.Build.Tasks] $(MetricsSupport)=false in "Release" (#9928)

Context: eb6397d
Context: 200f843
Context: dotnet/runtime#89880
Context: dotnet/aspire#4684
Context: dotnet/maui#24365
Context: https://github.com/jfversluis/MauiAspire

.NET 8 introduced use of System.Diagnostics.Metrics into `HttpClient`,
which immediately slowed down .NET for Android app startup times
(dotnet/runtime#89880).  This was "fixed" by *disabling* use of Metrics
within .NET for Android apps *by default* (eb6397d, 200f843).
Support for Metrics could be re-enabled by setting the
[`$(MetricsSupport)` MSBuild property][0].

.NET Aspire also uses System.Diagnostics.Metrics, and we'd like to
allow Metrics to be available by default in that environment; see also
dotnet/aspire#4684 and dotnet/maui#24365.

Update the `$(MetricsSupport)` MSBuild property to be false by default
only in "Release" configuration builds,, i.e. when `$(Optimize)`=true.

[0]: https://learn.microsoft.com/en-us/dotnet/core/deploying/trimming/trimming-options

Author: jfversluis

src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.DefaultProperties.targets

@@ -125,7 +125,7 @@
     <JsonSerializerIsReflectionEnabledByDefault Condition="'$(JsonSerializerIsReflectionEnabledByDefault)' == '' and '$(TrimMode)' == 'partial'">true</JsonSerializerIsReflectionEnabledByDefault>
     <!-- Set to disable throwing behavior, see: https://github.com/dotnet/runtime/issues/109724 -->
     <_DefaultValueAttributeSupport Condition="'$(_DefaultValueAttributeSupport)' == '' and '$(TrimMode)' == 'partial'">true</_DefaultValueAttributeSupport>
-    <MetricsSupport Condition="'$(MetricsSupport)' == ''">false</MetricsSupport>
+    <MetricsSupport Condition="'$(MetricsSupport)' == '' and '$(Optimize)' == 'true'">false</MetricsSupport>
     <AndroidAvoidEmitForPerformance Condition="'$(AndroidAvoidEmitForPerformance)' == ''">$(AvoidEmitForPerformance)</AndroidAvoidEmitForPerformance>
     <AndroidAvoidEmitForPerformance Condition="'$(AndroidAvoidEmitForPerformance)' == ''">true</AndroidAvoidEmitForPerformance>
     <!-- Verify DI trimmability at development-time, but turn the validation off for production/trimmed builds. -->

tests/Mono.Android-Tests/Mono.Android-Tests/System/AppContextTests.cs

@@ -39,7 +39,11 @@ public void GetData (string name, string expected)
 			new object [] {
 				/* className */    "System.Diagnostics.Metrics.Meter, System.Diagnostics.DiagnosticSource",
 				/* propertyName */ "<IsSupported>k__BackingField",
+#if DEBUG
+				/* expected */     true,
+#else   // !DEBUG
 				/* expected */     false,
+#endif  // !DEBUG
 			},
 		};