Update schema to include trimming-related properties & item types

[DamianEdwards]

Update src/MSBuild/MSBuild)/Microsoft.Build.CommonTypes.xsd with the various options and item types used for trimming, so that they show up in the MSBuild file editor in Visual Studio, e.g.:

• <TrimMode>
• <IsTrimmable>
• <SuppressTrimAnalysisWarnings>
• <EnableTrimAnalyzer>
• <TrimmerDefaultAction>
• <TrimmerSingleWarn>
• <ILLinkWarningLevel>
• <ILLinkTreatWarningsAsErrors>
• <TrimmerRemoveSymbols>
• <DebuggerSupport>
• <TrimmerRootAssembly />
• <TrimmerRootDescriptor />
• <TrimmableAssembly />
• more

@agocke