[Bug] Replace all uses of IsDesignerContext

[PureWeen]

Description

This check here

else if ($"{context}".Contains("com.android.layoutlib.bridge.android.BridgeContext"))

Is expensive and we should be able to achieve the same thing a couple different ways

• by checking IsInEditMode and setting it's result to a static variable
• We could also set a flag ImNotRunningInTheDesignerSoDontCallToString from FormsAppCompatActivity because Designer doesn't run any of the code inside FormsAppCompatActivity