Add [ActiveIf] decorator

[EricHu33]

Similar to ShowIf, Active the GUI if certain property met the requirement.

code for above gif

 Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
        [SubToggle(SurfaceOptions, _AlphaClip)]_AlphaClip ("Alpha Clipping", Float) = 0.0
        [ActiveIf(_AlphaClip, Equal, 1)]_Cutoff ("Alpha Clipping Threshold", Range(0.0, 1.0)) = 0.5
        _Other ("_Other", Float) = 0.0
        [SubToggle(SurfaceOptions, _AnotherToggle)]_AnotherToggle ("Another Toggle", Float) = 0.0
        [ActiveIf(_AnotherToggle, Equal, 1)]_Other2 ("_Other2", Float) = 0.0
    }

[JasonMa0012]

I will not merge it for the time being, because the latest branch is 2.x, the data structure has been greatly changed, and there is a lot of redundancy in these codes. I will refactor it when I have time.

[EricHu33]

I will not merge it for the time being, because the latest branch is 2.x, the data structure has been greatly changed, and there is a lot of redundancy in these codes. I will refactor it when I have time.

I understand :), I'll update to 2.x soon and see if I can propurse a better PR.