Handle 'inherit' value for shorthand properties

[liZe]

Fix #1007.

The first commit b18b67a fixes inherit for text-decoration.

Using @generic_expander is a good idea, because it handles a lot of things, including inherit and initial automatically, and could handle other values like unset and revert. Using @generic_expander requires to yield tokens, not computed values, but that’s a fair trade-off and we should use it everywhere it’s possible.

We can then test the inherit value for all the expanders, as it’s now done for text-decoration.

If anyone (@ckepper?) is interested in updating this PR to handle other expanders, don’t hesitate to add a comment!

Here are the properties that aren’t / weren’t supported:

• text-decoration (b18b67a)
• word-wrap (#1007 Make 'inherit' value work correctly for word-wrap #1525)
• page-break-after/before
• border-radius
• page-break-inside
• line-clamp
• flex-flow
• flex
• text-align

[liZe]

@ckepper Thanks for your contribution, it will be merged soon 💚.

If you’re interested in these features, don’t hesitate to review this PR and give some feedback! If there’s anything you don’t understand, just ask, I’ll be happy to help.