text: replace Family with Shaper, add Font, Face

There is now a single shaping implementation, Shaper, for all fonts, replacing
Family that only covered a single typeface.

A typeface is identified by a name, where the empty string denotes the
default typeface.

Font is introduced to specify a particular font from the typeface, style,
weight and size.

Face is changed to an interface for a particular layout and shaping method.
The text/shape package is renamed to text/opentype and contains a Face
implementation based on golang.org/x/image/font/sfnt.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

text/lru_test.go

@@ -0,0 +1,54 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+package text
+
+import (
+	"strconv"
+	"testing"
+
+	"gioui.org/op/paint"
+)
+
+func TestLayoutLRU(t *testing.T) {
+	c := new(layoutCache)
+	put := func(i int) {
+		c.Put(layoutKey{str: strconv.Itoa(i)}, nil)
+	}
+	get := func(i int) bool {
+		_, ok := c.Get(layoutKey{str: strconv.Itoa(i)})
+		return ok
+	}
+	testLRU(t, put, get)
+}
+
+func TestPathLRU(t *testing.T) {
+	c := new(pathCache)
+	put := func(i int) {
+		c.Put(pathKey{str: strconv.Itoa(i)}, paint.ClipOp{})
+	}
+	get := func(i int) bool {
+		_, ok := c.Get(pathKey{str: strconv.Itoa(i)})
+		return ok
+	}
+	testLRU(t, put, get)
+}
+
+func testLRU(t *testing.T, put func(i int), get func(i int) bool) {
+	for i := 0; i < maxSize; i++ {
+		put(i)
+	}
+	for i := 0; i < maxSize; i++ {
+		if !get(i) {
+			t.Fatalf("key %d was evicted", i)
+		}
+	}
+	put(maxSize)
+	for i := 1; i < maxSize+1; i++ {
+		if !get(i) {
+			t.Fatalf("key %d was evicted", i)
+		}
+	}
+	if i := 0; get(i) {
+		t.Fatalf("key %d was not evicted", i)
+	}
+}