[build] Unify $(LangVersion) to use defaults across projects (#10766)

In general, we should only need to set `$(LangVersion)` in a `netstandard2.0` project
to `latest`. Any project that is `net10.0`, `net11.0`, etc. should use the default
C# version that the .NET SDK recommends.

Co-authored-by: simonrozsival <374616+simonrozsival@users.noreply.github.com>

Author: Copilot

build-tools/xaprepare/xaprepare/xaprepare.csproj

@@ -4,7 +4,6 @@
   <PropertyGroup>
     <TargetFramework>$(DotNetStableTargetFramework)</TargetFramework>
     <OutputType>Exe</OutputType>
-    <LangVersion>$(LangVersion)</LangVersion>
     <RootNamespace>Xamarin.Android.Prepare</RootNamespace>
     <AssemblyName>xaprepare</AssemblyName>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>

src/Microsoft.Android.Sdk.Analysis/Microsoft.Android.Sdk.Analysis.csproj

@@ -5,7 +5,6 @@
 		<AppendTargetFrameworkToOutputPath>false</AppendTargetFrameworkToOutputPath>
 		<OutputPath>$(MicrosoftAndroidSdkAnalysisOutDir)</OutputPath>
 		<IsRoslynComponent>true</IsRoslynComponent>
-		<LangVersion>latest</LangVersion>
 		<EnforceExtendedAnalyzerRules>true</EnforceExtendedAnalyzerRules>
 		<AssemblyOriginatorKeyFile>..\..\product.snk</AssemblyOriginatorKeyFile>
 	</PropertyGroup>

src/Microsoft.Android.Sdk.Analysis/Tests/Microsoft.Android.Sdk.Analysis.Tests.csproj

@@ -2,7 +2,6 @@
   <Import Project="..\..\..\Configuration.props" />
   <PropertyGroup>
     <TargetFramework>$(DotNetStableTargetFramework)</TargetFramework>
-    <LangVersion>latest</LangVersion>
     <OutputPath>..\..\..\bin\Test$(Configuration)</OutputPath>
   </PropertyGroup>
   <ItemGroup>

src/Mono.Android.Runtime/Mono.Android.Runtime.csproj

@@ -13,7 +13,6 @@
     <EnableSingleFileAnalyzer>true</EnableSingleFileAnalyzer>
     <GenerateAssemblyInfo>false</GenerateAssemblyInfo>
     <ImplicitlyExpandDesignTimeFacades>false</ImplicitlyExpandDesignTimeFacades>
-    <LangVersion>10</LangVersion>
     <NoStdLib>true</NoStdLib>
     <Nullable>enable</Nullable>
     <ProduceReferenceAssembly>true</ProduceReferenceAssembly>