Require bug link for partial implementation

[caugner]

What type of issue is this?

Linter issue

What is the issue?

When a browser is marked as partially supporting a feature, we don't currently require a bug link, making it hard to check if the limitation was meanwhile resolved.

What behavior were you expecting?

For every support statement with partial_implementation: true, we should require a bug link, either in the notes (preferred) or in the impl_url.

What version(s) of BCD is the issue present in?

• The current BCD release
• The current version of the main branch

Do you have anything more you want to share?

The following Firefox support statement for css.selectors.highlight prompted this:

browser-compat-data/css/selectors/highlight.json

Lines 21 to 25 in 9ec9ff9

	"firefox": {
	"version_added": "140",
	"partial_implementation": true,
	"notes": "Cannot yet be used with `text-decoration` and `text-shadow`."
	},

Requiring a bug link would provide context, make it easier to check if the limitation is still valid, and identify the browser version in which it was fixed.