Add RequireComponent Helper

[diadas]

I would like to have a helper function for creating "RequireComponent"-Tags.

See: https://docs.unity3d.com/ScriptReference/RequireComponent.html

I imagine it like this when the cursor is on the field:
[ light bulb ] private Image _image;
Pressing on the light bulb, the following menu entry will be available:
"Require Component >"
Pressing this, [RequireComponent(typeof(Image))] will be added to the class
When pressing on the ">", the options "Assign at Start()" and "Assign at Awake()" appear.
Both will add the tag to the class and additionally add code to the according magic functions:

Assign at Start() =
void Start() { _image = GetComponent<Image>(); }
Assign at Awake() =
void Awake() { _image = GetComponent<Image>(); }

[diadas]

See also #356

[krasnotsvetov]

Partly implemented in #1152

[oxysoft]

Note this could also be triggered with a quick-fix on the RequireComponent attribute itself, rather than initiating it from a field in the class. (in case the user started his work there first)

[citizenmatt]

Closed with #1259