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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- [ X] `./mach test-tidy` does not report any errors
- [ ] These changes fix #__ (github issue number if applicable).
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- [ ] There are tests for these changes OR
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Replace &JSRef with JSRef in the bulk of the generated code. This will
remove a level of indirection throughout all DOM code.
This patch doesn't change methods implemented on JSRef<T> to take `self`
rather than `&self`, and it leaves a few other uses of &JSRef, but those
changes can be made incrementally.