deps,text,widget,font/opentype: [API] add harfbuzz-powered text shaper

This commit introduces a new text shaping infrastructure
powered by Benoit Kugler's Go source-port of harfbuzz.
This shaper can properly display complex scripts and RTL
text. This commit changes the signature of the text.Shaper
function, which is a breaking API change.

The new functionality is available via opentype.ParseHarfbuzz,
which configures a text.Shaper leveraging the new backend.

References: https://todo.sr.ht/~eliasnaur/gio/146
Signed-off-by: Chris Waldon <christopher.waldon.dev@gmail.com>

text/lru_test.go

@@ -24,10 +24,10 @@ func TestLayoutLRU(t *testing.T) {
 func TestPathLRU(t *testing.T) {
 	c := new(pathCache)
 	put := func(i int) {
-		c.Put(pathKey{str: strconv.Itoa(i)}, clip.PathSpec{})
+		c.Put(pathKey{str: strconv.Itoa(i), gidHash: uint64(i)}, Layout{Runes: Range{Count: i}}, clip.PathSpec{})
 	}
 	get := func(i int) bool {
-		_, ok := c.Get(pathKey{str: strconv.Itoa(i)})
+		_, ok := c.Get(pathKey{str: strconv.Itoa(i), gidHash: uint64(i)}, Layout{Runes: Range{Count: i}})
 		return ok
 	}
 	testLRU(t, put, get)