Option to not add units of measure

[stoyan]

Currently

a{width:1}

becomes

a{width:1px}

which breaks my UI by turning invalid CSS into a valid one.

(Of course the right thing to do is to fix my origin code to not contain invalid CSS. But in a large project that may take a while and hurt the adoption of LightningCSS.)

I think in this case the correct behavior would be to drop the property completely as its value is incorrect.

[devongovett]

Lightning CSS is a bit lenient here to support quirks mode, where unitless lengths are supported in some properties: https://drafts.csswg.org/css-values-4/#deprecated-quirky-length. Perhaps there should be an option to make this more strict, as mentioned in the code here:

lightningcss/src/values/length.rs

Lines 145 to 148 in 445def9

	Token::Number { value, .. } => {
	// TODO: quirks mode only?
	Ok(LengthValue::Px(value))
	}