Codegen: don't let Elm UI defaults to leak

[passiomatic]

Currently code emitter tries to reduce to write redundant values like: zero padding, zero spacing, "regular" font weight, etc.

This is great but for certain elements this causes to Elm UI to pick its default values in the generate Elm code. I'll keep the list updated with the values that needs to be specified even if they are zero:

• Padding for text fields
• ✅ Background color for text fields
• Border corner for text fields and buttons

This boils down to check for Node.type_ and decide what to do while emitting each style.