XFA -- Display text content

- display xhtml;
  - allow spaces in xhtml (xfa-spacerun:yes);
  - support column layout;
  - fix some border issues.

web/xfa_layer_builder.css

@@ -1,4 +1,4 @@
-*/* Copyright 2021 Mozilla Foundation
+/* Copyright 2021 Mozilla Foundation
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -30,6 +30,7 @@
   text-decoration: inherit;
   vertical-align: inherit;
   box-sizing: border-box;
+  background: transparent;
 }
 
 .xfaFont {
@@ -44,19 +45,23 @@
 }
 
 .xfaDraw {
-  z-index: 200;
+  z-index: 100;
 }
 
 .xfaExclgroup {
-  z-index: 300;
+  z-index: 200;
 }
 
 .xfaField {
   z-index: 300;
 }
 
+.xfaRich {
+  z-index: 300;
+}
+
 .xfaSubform {
-  z-index: 100;
+  z-index: 200;
 }
 
 .xfaLabel {
@@ -77,6 +82,7 @@
   height: 100%;
   flex: 1 1 auto;
   border: none;
+  resize: none;
 }
 
 .xfaLabel > input[type="checkbox"] {
@@ -123,6 +129,16 @@
   background: Highlight;
 }
 
+.xfaRich {
+  white-space: pre-wrap;
+}
+
+.xfaImage,
+.xfaRich {
+  width: 100%;
+  height: 100%;
+}
+
 .xfaLrTb,
 .xfaRlTb,
 .xfaTb,
@@ -134,6 +150,10 @@
   position: relative;
 }
 
+.xfaArea {
+  position: relative;
+}
+
 .xfaValignMiddle {
   display: flex;
   align-items: center;