Add image render tests

Add tests that will match rendered words/paragraphs against reference
images.

Use env var `GENERATE_IMAGES` to write the initial reference images to
the repository.

tests/shaping_and_rendering.rs

@@ -0,0 +1,75 @@
+use common::DrawTestCfg;
+use cosmic_text::Attrs;
+use fontdb::Family;
+
+mod common;
+
+#[test]
+fn test_hebrew_word_rendering() {
+    let attrs = Attrs::new().family(Family::Name("Noto Sans"));
+    DrawTestCfg::new("a_hebrew_word")
+        .font_size(36., 40.)
+        .font_attrs(attrs)
+        .text("בדיקה")
+        .canvas(100, 60)
+        .validate_text_rendering();
+}
+
+#[test]
+fn test_hebrew_paragraph_rendering() {
+    let paragraph = "השועל החום המהיר קופץ מעל הכלב העצלן";
+    let attrs = Attrs::new().family(Family::Name("Noto Sans"));
+    DrawTestCfg::new("a_hebrew_paragraph")
+        .font_size(36., 40.)
+        .font_attrs(attrs)
+        .text(paragraph)
+        .canvas(400, 110)
+        .validate_text_rendering();
+}
+
+#[test]
+fn test_english_mixed_with_hebrew_paragraph_rendering() {
+    let paragraph = "Many computer programs fail to display bidirectional text correctly. For example, this page is mostly LTR English script, and here is the RTL Hebrew name Sarah: שרה, spelled sin (ש) on the right, resh (ר) in the middle, and heh (ה) on the left.";
+    let attrs = Attrs::new().family(Family::Name("Noto Sans"));
+    DrawTestCfg::new("some_english_mixed_with_hebrew")
+        .font_size(16., 20.)
+        .font_attrs(attrs)
+        .text(paragraph)
+        .canvas(400, 120)
+        .validate_text_rendering();
+}
+
+#[test]
+fn test_arabic_word_rendering() {
+    let attrs = Attrs::new().family(Family::Name("Noto Sans"));
+    DrawTestCfg::new("an_arabic_word")
+        .font_size(36., 40.)
+        .font_attrs(attrs)
+        .text("خالصة")
+        .canvas(100, 60)
+        .validate_text_rendering();
+}
+
+#[test]
+fn test_arabic_paragraph_rendering() {
+    let paragraph = "الثعلب البني السريع يقفز فوق الكلب الكسول";
+    let attrs = Attrs::new().family(Family::Name("Noto Sans"));
+    DrawTestCfg::new("an_arabic_paragraph")
+        .font_size(36., 40.)
+        .font_attrs(attrs)
+        .text(paragraph)
+        .canvas(400, 110)
+        .validate_text_rendering();
+}
+
+#[test]
+fn test_english_mixed_with_arabic_paragraph_rendering() {
+    let paragraph = "I like to render اللغة العربية in Rust!";
+    let attrs = Attrs::new().family(Family::Name("Noto Sans"));
+    DrawTestCfg::new("some_english_mixed_with_arabic")
+        .font_size(36., 40.)
+        .font_attrs(attrs)
+        .text(paragraph)
+        .canvas(400, 110)
+        .validate_text_rendering();
+}