fix(styling): Fix annotation layer styling

src/common/BaseAnnotator.scss

@@ -30,3 +30,7 @@
     @include box-sizing;
     @include common-typography;
 }
+
+.ba-Layer--popup {
+    z-index: 4;
+}

src/drawing/DrawingAnnotations.scss

@@ -37,3 +37,7 @@
         pointer-events: none;
     }
 }
+
+.ba-Layer--drawing {
+    z-index: 3;
+}

src/highlight/HighlightAnnotations.scss

@@ -10,3 +10,7 @@
 .ba-HighlightAnnotations-popup {
     pointer-events: auto;
 }
+
+.ba-Layer--highlight {
+    z-index: 3;
+}

src/image/ImageAnnotator.scss

@@ -15,6 +15,6 @@
     // transform applied to each of the managers' react mount element to account for
     // rotation
     .ba-Layer--popup {
-        z-index: 1;
+        z-index: 4;
     }
 }

src/region/RegionAnnotation.scss

@@ -20,3 +20,7 @@
         @include ba-RegionRect-callout;
     }
 }
+
+.ba-Layer--region {
+    z-index: 3;
+}