Make test-layout use layout serialization

Now that we have this api, lets use it for
our tests.

tests/layouts/valid-1.layout

+{
+  "text" : "This is a test of the automatic emergency brake!\n",
+  "attributes" : [
+    {
+      "start" : 22,
+      "end" : 41,
+      "type" : "foreground",
+      "value" : "#00000000ffff"
+    },
+    {
+      "start" : 22,
+      "end" : 41,
+      "type" : "underline",
+      "value" : "single"
+    }
+  ],
+  "font" : "Cantarell 11",
+  "ellipsize" : "end",
+  "width" : 225280
+}

tests/layouts/valid-1.markup

-width=220,ellipsize=end
-This is a test of the <span foreground="#0000ff" underline="single">automatic emergency</span> brake!

tests/layouts/valid-10.layout

+{
+  "text" : "Hello שלום Γειά σας\n",
+  "attributes" : [],
+  "font" : "Cantarell 11",
+  "justify" : true,
+  "ellipsize" : "end",
+  "width" : 102400
+}

tests/layouts/valid-10.markup

-width=100,justify=true,ellipsize=end
-Hello שלום Γειά σας

tests/layouts/valid-11.layout

+{
+  "text" : "double low error\n",
+  "attributes" : [
+    {
+      "end" : 6,
+      "type" : "underline",
+      "value" : "double"
+    },
+    {
+      "end" : 6,
+      "type" : "overline",
+      "value" : "single"
+    },
+    {
+      "start" : 7,
+      "end" : 10,
+      "type" : "underline",
+      "value" : "low"
+    },
+    {
+      "start" : 7,
+      "end" : 10,
+      "type" : "strikethrough",
+      "value" : true
+    },
+    {
+      "start" : 11,
+      "end" : 16,
+      "type" : "underline",
+      "value" : "error"
+    },
+    {
+      "start" : 11,
+      "end" : 16,
+      "type" : "rise",
+      "value" : 1024
+    }
+  ],
+  "font" : "Cantarell 11",
+  "wrap" : "char",
+  "width" : 225280
+}

tests/layouts/valid-11.markup

-width=220,wrap=char
-<span underline='double' overline='single'>double</span> <span underline='low' strikethrough='true'>low</span> <span underline='error' rise='1024'>error</span>

tests/layouts/valid-12.layout

+{
+  "text" : "a       b       c       d
e     f       g       h\n",
+  "attributes" : [],
+  "font" : "Cantarell 11",
+  "tabs" : {
+    "positions-in-pixels" : true,
+    "positions" : [
+      0,
+      50,
+      100,
+      150,
+      200
+    ]
+  }
+}

tests/layouts/valid-12.markup

-wrap=word,tabs=0 50 100 150 200
-a       b       c       d
e     f       g       h

tests/layouts/valid-13.layout

+{
+  "text" : "a       b       c       d
e     f       g       h\n",
+  "attributes" : [],
+  "font" : "Cantarell 11",
+  "tabs" : {
+    "positions-in-pixels" : true,
+    "positions" : [
+      0,
+      50,
+      100,
+      150,
+      200
+    ]
+  },
+  "single-paragraph" : true
+}

tests/layouts/valid-13.markup

-wrap=word,tabs=0 50 100 150 200,single_paragraph=true
-a       b       c       d
e     f       g       h

tests/layouts/valid-14.layout

+{
+  "text" : "你好 Hello שלום Γειά σας\n",
+  "attributes" : [],
+  "font" : "Cantarell 11",
+  "ellipsize" : "start",
+  "width" : 161792,
+  "line-spacing" : 1.5
+}

tests/layouts/valid-14.markup

-line_spacing=1.5,width=158,ellipsize=start
-你好 Hello שלום Γειά σας

tests/layouts/valid-15.layout

+{
+  "text" : "Lets see if this text is long enough to wrap due to height limitations. It might, or it might not.\n",
+  "attributes" : [],
+  "font" : "Cantarell 11",
+  "ellipsize" : "end",
+  "width" : 153600,
+  "height" : 40960
+}

tests/layouts/valid-15.markup

-ellipsize=end,height=40,width=150
-Lets see if this text is long enough to wrap due to height limitations. It might, or it might not.

tests/layouts/valid-16.layout

+{
+  "text" : "Lets see if this text is long enough to wrap due to height limitations. It might, or it might not.\n",
+  "attributes" : [],
+  "font" : "Cantarell 11",
+  "wrap" : "word-char",
+  "ellipsize" : "end",
+  "width" : 153600,
+  "height" : -2
+}

tests/layouts/valid-16.markup

-wrap=word-char,ellipsize=end,width=150,height=-2
-Lets see if this text is long enough to wrap due to height limitations. It might, or it might not.

tests/layouts/valid-17.layout

+{
+  "text" : "some|bla|bla|bla\n",
+  "attributes" : [],
+  "font" : "Cantarell 11",
+  "justify" : true,
+  "width" : 102400
+}

tests/layouts/valid-17.markup

-justify=true,width=100
-some|bla|bla|bla

tests/layouts/valid-18.layout

+{
+  "text" : "some line breaks
and mis­ce­llaneous ignora‌bles\n",
+  "attributes" : [
+    {
+      "end" : 57,
+      "type" : "show",
+      "value" : 7
+    }
+  ],
+  "font" : "Cantarell 11"
+}

tests/layouts/valid-18.markup

-
-<span show="spaces|line-breaks|ignorables">some line breaks
and mis­ce­llaneous ignora‌bles</span>