Probe directory tree for wildcard matching

[KyleJu]

Fix web-platform-tests/wpt-metadata#4665 and a part of #3448. Probe directory tree for wildcard matching, regardless if a match has found.

It should not have much performance impact before and after the change.

[jcscottiii]

The code LGTM. Could you monitor the performance of this? Now we are always walking up to the root (which is needed for this implementation). If it is bad, we may need a way to improve this look up

[KyleJu]

The code LGTM. Could you monitor the performance of this? Now we are always walking up to the root (which is needed for this implementation). If it is bad, we may need a way to improve this look up

Yup that is a good call. The reason for my "It should not have much performance impact before and after the change." is because the algorithm before this change always walks up the root, as most tests don't have a label. In terms of optimization, we could pre-build a tree-like structure against wpt-metadata, traverse the tree from the root directory and accumulate all the labels as it walks down. So it is a constant lookup. E.g.

	metadata := map[string][]string{
		"/foo/bar/b.html": {"random"},
		"/a/*":  {"interop1", "INTEROP2"},
		"/d/e/f":          {""},
		"/a/b/c.html:  {"foo"},
		"/a/b/d.html:  {"bar"},
	}

will result in (remove the wildcards along the way

	metadataTree := map[string][]string{
		"/foo/bar/b.html": {"random"},
		"/d/e/f":          {""},
		"/a/b/c.html":  {"foo", "interop1", "INTEROP2"},
		"/a/b/d.html::  {"bar", "interop1", "INTEROP2"},
	}