Auto merge of #13969 - bbansalWolfPack:master, r=jdm

html form validation initial steps with  test html file

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Added code for initial steps in html form validation.
1. Added methods for trait validatable
2. implemented stub methods for  elements like HTMLInputElement, HTMLButtonElement, etc

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components/script/dom/htmltextareaelement.rs

@@ -406,4 +406,5 @@ impl VirtualMethods for HTMLTextAreaElement {
 
 impl FormControl for HTMLTextAreaElement {}
 
+
 impl Validatable for HTMLTextAreaElement {}