add RequiresUniqueFilePathSuffix in the HttpCapabilitiesBase

[birojnayak]

This is used in System.Web which I porting via CoreWebForm for the control PageAdapter.cs here

public virtual bool [RequiresUniqueFilePathSuffix](https://referencesource.microsoft.com/System.Web/R/1ee07db92c422b69.html) {
            get {
                if (![_haveRequiresUniqueFilePathSuffix](https://referencesource.microsoft.com/System.Web/Configuration/HttpCapabilitiesBase.cs.html#05cda9980015c420)) {
                    [_requiresUniqueFilePathSuffix](https://referencesource.microsoft.com/System.Web/Configuration/HttpCapabilitiesBase.cs.html#c63bb5d48aface99) = [CapsParseBoolDefault](https://referencesource.microsoft.com/System.Web/Configuration/HttpCapabilitiesBase.cs.html#e84f53ec79816a14)("requiresUniqueFilePathSuffix", false);
                    [_haveRequiresUniqueFilePathSuffix](https://referencesource.microsoft.com/System.Web/Configuration/HttpCapabilitiesBase.cs.html#05cda9980015c420) = true;
                }
                return [_requiresUniqueFilePathSuffix](https://referencesource.microsoft.com/System.Web/Configuration/HttpCapabilitiesBase.cs.html#c63bb5d48aface99);
            }
        }