SetPixels Analyzer

[sailro]

Fixes #55

Checklist

• I have read the Contribution Guide ;
• There is an approved issue describing the change when contributing a new analyzer or suppressor ;
• I have added tests that prove my fix is effective or that my feature works ;
• I have added necessary documentation (if appropriate) ;

Declare a simple attribute and a rule:

public class SetPixelsMethodUsageAttribute : MethodUsageAttribute
{
}

public class SetPixelsMethodUsageAnalyzer : BaseMethodUsageAnalyzer<SetPixelsMethodUsageAttribute> 
{
	internal static readonly DiagnosticDescriptor Rule = new DiagnosticDescriptor(
		id: "UNT0017",
		title: Strings.SetPixelsMethodUsageDiagnosticTitle,
		messageFormat: Strings.SetPixelsMethodUsageDiagnosticMessageFormat,
		category: DiagnosticCategory.Performance,
		defaultSeverity: DiagnosticSeverity.Info,
		isEnabledByDefault: true,
		description: Strings.SetPixelsMethodUsageDiagnosticDescription);

	public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics => ImmutableArray.Create(Rule);
}

Then decorate stubs to trigger analysis:

class Texture2D
{
	[SetPixelsMethodUsage] void SetPixels(int x, int y, int blockWidth, int blockHeight, Color[] colors, int miplevel) { }
	[SetPixelsMethodUsage] void SetPixels(int x, int y, int blockWidth, int blockHeight, Color[] colors) { }
	[SetPixelsMethodUsage] void SetPixels(Color[] colors, int miplevel) { }
	[SetPixelsMethodUsage] void SetPixels(Color[] colors) { }
}

Should be very easy to reuse to flag method that allocates.