Map CSS global keywords

[Elchi3]

Currently, the CSS test builder just ignores global keywords:

mdn-bcd-collector/test-builder/css.ts

Lines 342 to 354 in 8947904

	for (const val of resolveValuesFromTypes(input, types)) {
	if (
	[
	"inherit",
	"initial",
	"revert",
	"revert-layer",
	"unset",
	...ignoredColorNames,
	].includes(val)
	) {
	// Skip generic property values
	continue;

We should have tests for these and map the results to BCD's structure which put this data under css.types.global_keywords.*