Enlarge the HTML content block size

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When using the HTML content block, we always have to resize the `textarea` to be able to see the html code and modify it. It's not something problematic but it's tedious, since we always have to come back and forth to see the content block and modify it again.

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I would like that the `textarea` resizes to fit the content or, at least, have some "air".

We could use the field-sizing css property, that it's not fully supported yet, but that it does not break anything, or at least give a "row" of 10~15.

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Add rows to the content of the textarea.

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Could this issue impact on users private data?

No

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