fix(runtime-dom): <img> width should be set as attribute

[zh-lx]

close #8780

[TheDutchCoder]

Setting 24px as an attribute is not valid HTML: https://developer.mozilla.org/en-US/docs/Web/HTML/Element/img

The intrinsic height of the image, in pixels. Must be an integer without a unit

So I think if anything, it should be parsed as an integer, not blindly propagated with invalid values?

[zh-lx]

I have known this standard, but in most browsers, it can be rendered normally when set 24px with unit. So my main point is that when user give an invalid value, vue should keep the invalid value and let browser to handle the invalid value, rather than rewrite it to 0 in vue.

[TheDutchCoder]

Ok that's a fair point, I guess normally Vue also propagates invalid attribute values, so that's at least consistent 👍