Add missing css.properties.display.flow feature

[queengooborg]

This PR adds the missing flow member of the display CSS property. The data comes from the mdn-bcd-collector project (v10.12.3).

Check out the collector's guide on how to review this PR.

Tests Used: https://mdn-bcd-collector.gooborg.com/tests/css/properties/display/flow

[caugner]

I think we'd need to test manually that display: flow has the specified effect.

[caugner]

According to https://bugzil.la/1657594, Firefox may not actually support it:

The Compatibility panel should indicate that display: flow is converted to display:block in Firefox,

[caugner]

Discussed with Vinyl, and the question is whether it's always display:block, or if it is converted to the default value for the element (e.g. display: inline for <span>)

[caugner]

So I generated a test case with ChatGPT: https://developer.mozilla.org/de/play?id=h%2BLlW3ImqADHCJYkMw2xE%2BjFSvlfWApNyUj1hSyEa2VSWUgXOu84ObYg3ftPQZ74pE8GnTGvbE18Lg0V

Tested in Chrome 131, Firefox Nightly 134.0a1 (2024-11-21), and Safari 18.1.1.

All browsers do not seem to support flow, i.e. the computed value is block.

But maybe that's in accordance to the spec:

Otherwise it generates a block container box.

So I came up with another (ChatGPT-generated) test case that sets style.display and reads it again: https://developer.mozilla.org/en-US/play?id=UGBq0JaWyjIGJz8nqIEbFux3a3rDR5mS3uppv7pl%2Bn03MxTNx0%2B%2BXNGDjtIzkD0ICNQbWIjuTJQKhQJm

And this test also fails in all three browsers engines. 🤔

[caugner]

See: openwebdocs/mdn-bcd-collector#1975

[caugner]

Looking at the table in the spec, it looks like block and inline are short-hands for block flow and inline flow respectively, and Chrome/Firefox/Safari all treat flow as a short-hand for block [flow], cf. https://developer.mozilla.org/play?id=4XlsKP4CqpgoFbNBvZ%2Fjgtkg%2FUL9Cy5Ir3eUKVZ3qiDu5M%2FDXudS5E6Em63jaaKmFyFsQ6x5pJ4x9sES.

This is in accordance with the spec:

If a <display-outside> value is specified but <display-inside> is omitted, the element’s inner display type defaults to flow.
If a <display-inside> value is specified but <display-outside> is omitted, the element’s outer display type defaults to block—​except for ruby, which defaults to inline.

@queengooborg Was your intention to document flow layout support (likely supported from the beginning), or support for the flow value (as a short-hand for block flow or block)?